Patent Publication Number: US-2013232356-A1

Title: Electrical power saving system

Description:
This application is a divisional application of application Ser. No. 12/866,967, which is the National Stage of International Application No. PCT/JP2009/000550, filed Feb. 12, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to an electrical power saving system, and particularly relates to an AV system and an AV apparatus control method in which electricity consumption of the system is controlled by switching operation modes of apparatuses connected via a communication network. 
     2. Description of Related Art 
     Conventionally, there is an Audio/Visual (AV) system in which a video recording and reproduction apparatus such as a Digital Versatile Disc (DVD) recorder is connected to a television receiver (hereafter referred to as “TV”). In the AV system, video and audio are viewed, and an external AV amplifier and an external speaker are further connected to output audio from the external speaker. In order to view and operate each apparatus in such an AV system, the user needs to perform an operation of input selection or reproduction by separately using a remote controller (hereafter referred to as “remote control”) corresponding to the apparatus. This requires a complex operation. 
     One method for solving this problem is a method that employs a High-Definition Multimedia Interface (HDMI) standard. In HDMI, a feature named Consumer Electronics Control (CEC) is defined (Non-patent Reference 1). CEC is a feature that connects a TV and various AV apparatuses by HDMI cables, and controls the AV apparatuses using CEC commands which enable bidirectional control command transmission and reception, via CEC buses included in the HDMI cables. 
     Moreover, the HDMI standard has a feature that a reproduction apparatus such as a DVD recorder can read reproduction capability information of a connected apparatus to adapt video and audio data to an output format of the connected apparatus or encrypt the video and audio data, and transmit the video and audio data. 
     For example, reproduction capability information is transferred from an apparatus (hereafter referred to as “HDMI input apparatus”) including a HDMI input unit, such as a TV or an AV amplifier, to an apparatus (hereafter referred to as “HDMI output apparatus”) to which the HDMI input apparatus is connected, using a Display Data Channel (DDC) bus that is a unidirectional connection. “DDC” mentioned here is a standard created by the Video Electronics Standards Association (VESA) as a feature of communicating model information and the like of a display to the HDMI output apparatus, in order to achieve plug and play for the display. Information transferred by DDC includes model information and a reproducible image and audio format of the HDMI input apparatus, a physical address assigned to the HDMI apparatus, and so on. 
     In the HDMI standard, a logical address (hereafter “LA”) and a physical address (hereafter “PA”) are defined for each apparatus, for communication by CEC commands. 
     A PA is an address determined so as to reflect a connection topology of the HDMI output apparatus, and is unidirectionally transmitted from the HDMI input apparatus to the HDMI output apparatus. The PA is determined by adding a value that differs for each HDMI input unit, to a PA obtained by the HDMI input apparatus. 
     An apparatus that includes both a HDMI input unit and a HDMI output unit, such as an AV amplifier, obtains a PA of the AV amplifier itself from an apparatus to which the HDMI output unit is connected. The AV amplifier then adds a value corresponding to the HDMI input unit to the obtained PA, thereby determining a PA of a HDMI output apparatus connected to the AV amplifier. Accordingly, a PA of an apparatus (hereafter “root apparatus”) that includes a HDMI input unit and serves as a root is determined hierarchically as “0. 0. 0. 0”. 
     For instance, a TV that includes no HDMI output unit and only includes a HDMI input unit always has the PA “0. 0. 0. 0”, as a root apparatus. A PA of an apparatus connected to the root apparatus is determined in such a manner that, as an example, a PA of an apparatus connected to a first HDMI input unit of the root apparatus is “1. 0. 0. 0” and a PA of an apparatus connected to a second HDMI input unit of the root apparatus is “2. 0. 0. 0”. 
     An apparatus that includes both an input unit and an output unit further determines a PA for each input unit, from a PA of the apparatus itself. As an example, a PA of an apparatus connected to a first input unit of the apparatus having the PA “1. 0. 0. 0” is “1. 1. 0. 0”, and a PA of an apparatus connected to a second input unit of the apparatus having the PA “1. 0. 0. 0” is “1. 2. 0. 0”. 
     On the other hand, a LA is assigned to each CEC-capable apparatus connected via HDMI, and used as a destination address for CEC command transmission and reception. 
     In CEC, there are a command that is transmitted to a designated destination, and a broadcast command that is notified to all CEC-capable apparatuses connected via HDMI. Communication is performed by combining these commands in CEC. 
     Note that a CEC command is made up of a LA of a transmitter apparatus, a LA of a destination apparatus, an opcode, and an operand. 
     Furthermore, HDMI defines control commands such as &lt;Active Source&gt; for performing input selection, &lt;Standby&gt; for powering OFF an apparatus, &lt;Give Power Status&gt; for querying a power state of an apparatus, &lt;Polling Message&gt; for ascertaining whether or not an apparatus of a destination LA is present on a communication network, and &lt;Vendor Command&gt; enabling each manufacturer to independently define an apparatus operation. In HDMI, various cooperative operations can be realized by transmitting and receiving these control commands in combination between CEC-capable apparatuses connected via HDMI. 
     Non-patent Reference 1: High-Definition Multimedia Interface Specification Version 1.3a 
     SUMMARY OF THE INVENTION 
     1. Problems that Invention is to Solve 
     In CEC, the &lt;Standby&gt; command is defined as a command for powering OFF a connected apparatus, An apparatus such as a DVD recorder has a plurality of operation states even in a power-OFF state. These operation states differ in electricity consumption. 
     In conventional techniques, however, it is impossible to control the plurality of operation states in the connected apparatus. This causes inefficient consumption of electricity as in the case where, even when the user is not using an apparatus, a function in the apparatus is energized. In order to improve electricity consumption efficiency by a user operation, the user needs to switch the operation state of each connected apparatus by operating a button or a remote control of the apparatus. This requires a complex operation for the user. 
     Besides, in order to check an amount of electricity consumption of the apparatus, the user needs to newly connect a watt-hour meter or the like and perform measurement. Thus, a complex operation is needed for improving electricity consumption efficiency. 
     The present invention has been made in view of the above problems, and has an object of realizing an electrical power saving system that achieves efficient electricity consumption of apparatuses connected via a communication network. 
     2. Means to Solve the Problems 
     To solve the above problems, an electrical power saving system according to the present invention is an electrical power saving system including at least a first apparatus and a second apparatus that are connected to each other via a communication network, each of the first apparatus and the second apparatus including: a transmission and reception unit that transmits and receives a control command via the communication network, the control command being a command by which one apparatus controls another apparatus; and an operation state switching unit that switches an operation state according to the control command, wherein each of the first apparatus and the second apparatus has at least a first OFF operation mode and a second OFF operation mode as operation states that differ in electricity consumption, the first OFF operation mode being an operation state in which the apparatus is in a power-OFF state but a part of the apparatus is supplied with power, and the second OFF operation mode being an operation state of lower electricity consumption than the first OFF operation mode, and the operation state switching unit in the second apparatus switches the operation state of the second apparatus from the first OFF operation mode to the second OFF operation mode in the case where, when the second apparatus is in the first OFF operation mode, the transmission and reception unit in the second apparatus receives a control command instructing to switch the operation state, from the first apparatus. 
     In this way, an operation state of a connected apparatus can be switched by a control command of another apparatus and the like. Hence, in a system where a plurality of apparatuses that each have a plurality of operation states of different electricity consumption are connected via a communication network such as HDMI, the operation state of the plurality of apparatuses can be controlled so as to improve electricity consumption efficiency. This makes it possible to realize an electrical power saving system that achieves efficient electricity consumption of apparatuses connected via a communication network. 
     Preferably, the second apparatus further includes a timer unit that counts an elapse of a predetermined time, wherein the operation state switching unit in the second apparatus switches the operation state of the second apparatus from the first OFF operation mode to the second OFF operation mode, when the timer unit counts the elapse of the predetermined time during which the second apparatus is in the first OFF operation mode. Here, the second apparatus may further include a determination unit that determines the operation state of the first apparatus according to the control command transmitted and received by the transmission and reception unit in the second apparatus, wherein the transmission and reception unit in the first apparatus transmits, as the control command, a control command including the operation state of the first apparatus, to the second apparatus, and the operation state switching unit in the second apparatus switches the operation state of the second apparatus from the first OFF operation mode to the second OFF operation mode in the case where, when the second apparatus is in the first OFF operation mode, the determination unit determines that the first apparatus is in an operation state in which the first apparatus is in a power-OFF state, the operation state in which the first apparatus is in a power-OFF state including the first OFF operation mode and the second OFF operation mode. 
     In this way, the operation state of the apparatus can be switched not only by the control command of another apparatus, but also by using the elapse of the time set in the apparatus or the state of another apparatus as a trigger. 
     Moreover, to solve the above problems, an electrical power saving system according to the present invention is an electrical power saving system including at least a video display apparatus and a video recording apparatus that are connected to each other via a communication network, each of the video display apparatus and the video recording apparatus including: a transmission and reception unit that transmits and receives a control command via the communication network, the control command being a command by which one apparatus controls another apparatus; and an operation state switching unit that switches an operation state according to the control command, wherein each of the video display apparatus and the video recording apparatus has at least a first OFF operation mode and a second OFF operation mode as operation states that differ in electricity consumption, the first OFF operation mode being an operation state in which the apparatus is in a power-OFF state but a part of the apparatus is supplied with power, and the second OFF operation mode being an operation state of lower electricity consumption than the first OFF operation mode, and the operation state switching unit in the video recording apparatus switches the operation state of the video recording apparatus from the first OFF operation mode to the second OFF operation mode in the case where, when the video recording apparatus is in the first OFF operation mode, the transmission and reception unit in the video recording apparatus receives a control command instructing to switch the operation state, from the video display apparatus. 
     Note that the present invention can be realized not only as a system, but also as an apparatus or an integrated circuit including processing units of the system, or a method including steps that correspond to the processing units of the system. 
     3. Effects of the Invention 
     According to the present invention, it is possible to realize an electrical power saving system that achieves efficient electricity consumption of connected apparatuses. 
     In detail, by switching an operation state of a connected apparatus by a simple user operation and the like so as not to energize an unused function, an electrical power saving system that achieves efficient electricity consumption of apparatuses connected via a communication network can be realized. 
     Moreover, there is also an advantageous effect that the user can check an amount of electricity consumption measured without connecting a new apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural diagram of an AV system in a first embodiment of the present invention. 
         FIG. 2  is a functional block diagram of a TV  10  in the first embodiment of the present invention. 
         FIG. 3  is a functional block diagram of a DVD recorder  20  in the first embodiment of the present invention. 
         FIG. 4  is a functional block diagram of a set-top box  30  in the first embodiment of the present invention. 
         FIG. 5A  is a diagram showing a correspondence table of operation modes and functions in the DVD recorder  20  in the first embodiment of the present invention. 
         FIG. 5B  is a diagram showing a correspondence table of operation modes and functions in the set-top box  30  in the first embodiment of the present invention. 
         FIG. 5C  is a diagram showing a correspondence table of operation modes and functions in the TV  10  in the first embodiment of the present invention. 
         FIG. 6  is a diagram showing an example of a menu for setting an operation mode and a function in the DVD recorder  20  in the first embodiment of the present invention. 
         FIG. 7  is a diagram showing an example of an operation mode switching time setting method by an OSD menu display in the TV  10  in the first embodiment of the present invention. 
         FIG. 8  is a diagram showing an example of a mode switching time setting table in the TV  10  in the first embodiment of the present invention. 
         FIG. 9  is a diagram showing an example of a flow of CEC command transmission and reception when the DVD recorder  20  and the set-top box  30  operate according to a user operation in the first embodiment of the present invention. 
         FIG. 10  is a diagram showing an example of correspondence of operation states and electricity consumption in the DVD recorder  20  in the first embodiment of the present invention. 
         FIG. 11  is a diagram showing an example of changes in operation and electricity consumption of the DVD recorder  20  in the first embodiment of the present invention. 
         FIG. 12  is a diagram showing an example of displaying an operation state of each apparatus and a total amount of electricity consumption in the AV system, in the TV  10  in the first embodiment of the present invention. 
         FIG. 13  is a structural diagram of an AV system in a second embodiment of the present invention. 
         FIG. 14  is a functional block diagram of a TV  50  in the second embodiment of the present invention. 
         FIG. 15  is a functional block diagram of a DVD recorder  60  in the second embodiment of the present invention. 
         FIG. 16  is a functional block diagram of a set-top box  70  in the second embodiment of the present invention. 
         FIG. 17  is a diagram showing an example of an OSD menu for setting a function that is operational in an operation mode  3  and switching to the operation mode  3 , in the TV  50  in the second embodiment of the present invention. 
         FIG. 18  is a diagram showing an example of a flow of CEC command transmission and reception when the DVD recorder  60  and the set-top box  70  operate according to a user operation in the second embodiment of the present invention. 
         FIG. 19  is a diagram: showing an example of an OSD display for notifying the user of power OFF, in the TV  50  in the second embodiment of the present invention. 
         FIG. 20  is a diagram: showing an example of an OSD display for notifying the user of an amount of saved electricity consumption, in the TV  50  in the second embodiment of the present invention. 
         FIG. 21  is a structural diagram of an AV system including an AV amplifier  65 . 
         FIG. 22  is a diagram showing an example of a correspondence table of operation modes and functions in the AV amplifier  65 . 
     
    
    
     NUMERICAL REFERENCES 
     
         
         
           
               10 ,  50  TV 
               20 ,  60  DVD recorder 
               30 ,  70  Set-top box 
               40  Remote control 
               65  AV amplifier 
               101 ,  201 ,  301 ,  501  Operation mode switching timer 
               102 ,  202 ,  302 ,  502  Electricity consumption amount storage unit 
               103 ,  203 ,  303 ,  503  Saved electricity consumption amount storage unit 
               104 ,  204 ,  304  Electricity consumption storage unit 
               105 ,  205 ,  305  Remote control reception unit 
               106  Video output unit 
               107  Audio output unit 
               108  Active source apparatus storage unit 
               208 ,  308  Active source state storage unit 
               109  Connected apparatus list storage unit 
               110 ,  210 ,  310 ,  510 ,  610 ,  710  Microcomputer 
               111 ,  211 ,  311 ,  511 ,  611 ,  711  CEC communication unit 
               112  TMDS decoding unit 
               212 ,  312  Decoding unit 
               113  TMDS input unit 
               114 ,  115  HDMI input unit 
               214 ,  314  HDMI output unit 
               120 ,  220 ,  320  Tuner 
               121 ,  221 ,  321  Operation function setting storage unit 
               122 ,  222 ,  322  Operation state storage unit 
               216 ,  316  TV power state determination unit 
               217  Recording timer 
               218  IP communication unit 
               219  Recording unit 
           
         
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following describes embodiments of an AV system and an AV apparatus control method according to the present invention in detail, with reference to drawings. 
     First Embodiment 
     Structure 
       FIG. 1  is a diagram schematically showing a structure of an AV system in a first embodiment.  FIG. 2  is a functional block diagram of a TV  10  in the first embodiment.  FIG. 3  is a functional block diagram of a DVD recorder  20  in the first embodiment.  FIG. 4  is a functional block diagram of a set-top box  30  in the first embodiment. 
     Note that the TV  10  in the first embodiment is an example of a first apparatus according to the present invention, and each of the DVD recorder  20  and the set-top box  30  in the first embodiment is an example of a second apparatus according to the present invention. 
     As shown in  FIG. 1 , the AV system in the first embodiment includes the TV  10 , the DVD recorder  20 , and the set-top box  30 . The AV system also includes, for example, a remote control  40 . 
     In the AV system, the DVD recorder  20  and the set-top box  30  are connected to the TV  10  via HDMI cables. CEC lines in HDMI are connected in a CEC communication unit  111  in the TV  10 . The TV  10 , the DVD recorder  20 , and the set-top box  30  are capable of performing transmission and reception of a CEC command as a control command with each other. 
     The TV  10  is an apparatus that outputs video and audio outputted from an apparatus connected via a HDMI cable, and a broadcast signal received via an antenna (not shown). 
     The TV  10  includes an operation mode switching timer  101 , an electricity consumption amount storage unit  102 , a saved electricity consumption amount storage unit  103 , an electricity consumption storage unit  104 , a remote control reception unit  105 , a video output unit  106 , an audio output unit  107 , an active source apparatus storage unit  108 , a connected apparatus list storage unit  109 , a microcomputer  110 , the CEC communication unit  111 , a TMDS decoding unit  112 , a TMDS input unit  113 , HDMI input units  114  and  115 , a tuner  120 , an operation function setting storage unit  121 , and an operation state storage unit  122 . 
     The operation mode switching timer  101  includes a timer and an operation mode switching time storage unit. 
     The operation mode switching timer  101  stores a time  1  to switch to an operation mode  1  and a time  2  to switch to an operation mode  2 , via the microcomputer  110 . When the time  1  or the time  2  is reached, the operation mode switching timer  101  notifies the microcomputer  110  that the corresponding set time is reached. 
     The electricity consumption amount storage unit  102  includes a current-day storage unit that temporarily stores an amount of electricity consumption of a current day, and a log recording unit that stores an amount of electricity consumption of a past fixed time period. Note that the log recording unit in the electricity consumption amount storage unit  102  is composed of a nonvolatile storage device. 
     The saved electricity consumption amount storage unit  103  includes a current-day storage unit that temporarily stores an amount of saved electricity consumption of the current day, and a log recording unit that stores an amount of saved electricity consumption of the past fixed time period. Note that the log recording unit in the saved electricity consumption amount storage unit  103  is composed of a nonvolatile storage device. 
     The electricity consumption storage unit  104  stores electricity consumption in each of a plurality of operation states of the TV  10 . 
     The remote control reception unit  105  receives a signal transmitted from the remote control  40 , and notifies the microcomputer  110  of the signal. Here, as an input unit, the remote control  40  includes a plurality of buttons such as a power button, a menu display button, and up, down, left, and right buttons, and a remote control signal transmission unit. 
     The video output unit  106  is a display unit, and displays video outputted from the TMDS decoding unit  112  or the tuner  120 . The video output unit  106  also performs On Screen Display (OSD) by superimposing a message and a menu on input video, according to a notification from the microcomputer  110 . 
     The audio output unit  107  is a speaker unit, and outputs audio outputted from the TMDS decoding unit  112  or the tuner  120 . 
     The active source apparatus storage unit  108  stores, when the CEC communication unit  111  receives an &lt;Active Source&gt; command from another apparatus, a LA and a PA of the apparatus transmitting the command. When the CEC communication unit  111  transmits an &lt;Active Source&gt; command, on the other hand, the active source apparatus storage unit  108  stores information that the TV  10  is an active source. 
     The connected apparatus list storage unit  109  receives a response to a &lt;Polling Message&gt; command transmitted by the CEC communication unit  111  and a command from another apparatus, and stores a list of apparatuses connected to the communication network. 
     The microcomputer  110  is a device that executes a program. The microcomputer  110  receives a notification from any of the operation mode switching timer  101 , the remote control reception unit  105 , and the CEC communication unit  111 . Upon receiving the notification, the microcomputer  110  reads or writes information in each storage unit such as the electricity consumption amount storage unit  102 , the saved electricity consumption amount storage unit  103 , the electricity consumption storage unit  104 , the active source apparatus storage unit  108 , the connected apparatus list storage unit  109 , the operation function setting storage unit  121 , and the operation mode switching timer  101 , and also controls the CEC communication unit  111 , the tuner  120 , the video output unit  106 , and the like. The microcomputer  110  also controls various functions of the TV  10  not shown. 
     The CEC communication unit  111  is an example of a device that transmits and receives a control command via the communication network. The CEC communication unit  111  performs transmission and reception of a CEC command. 
     The HDMI input unit  114  is a HDMI input port. In this embodiment, the HDMI input unit  114  is HDMI-connected with the DVD recorder  20 , and performs reception of video and audio data and bidirectional communication of a control message. The HDMI input unit  114  is used for transmission of a HPD signal  114 _ 1 , a DDC signal  114 _ 2 , a TMDS signal  114 _ 3 , and a CEC signal  114 _ 4 . 
     The HDMI input unit  115  is a HDMI input port. In this embodiment, the HDMI input unit  115  is HDMI-connected with the set-top box  30 , and performs reception of video and audio data and bidirectional communication of a control message. The HDMI input unit  115  is used for transmission of a HPD signal  115 _ 1 , a DDC signal  115 _ 2 , a TMDS signal  115 _ 3 , and a CEC signal  115 _ 4 . 
     Here, the HDMI input units  114  and  115  are not limited to HDMI. For instance, the HDMI input units  114  and  115  may each be an interface corresponding to an adapted communication mode or the like that provides the function described above, regardless of whether it is wired or wireless. 
     The TMDS input unit  113  receives TMDS data using the TMDS signal  114 _ 3  or  115 _ 3  of the HDMI input unit  114  or  115 , and outputs the TMDS data to the TMDS decoding unit  112 . 
     The TMDS decoding unit  112  TMDS-decodes the TMDS data, and outputs decoded video data to the video output unit  106  and decoded audio data to the audio output unit  107 . 
     The tuner  120  decodes a broadcast signal received via an antenna (not shown). The tuner  120  outputs decoded video data to the video output unit  106 , and decoded audio data to the audio output unit  107 . 
     The operation function setting storage unit  121  stores a table showing correspondence between various operation states and various functions of the TV  10 , as shown in  FIG. 5C . Note that the functions of the TV  10  shown in  FIG. 5C  are merely an example, and the present invention is not limited to these functions, so long as all functions of the TV  10  are associated with operation states. 
     The operation state storage unit  122  is a storage device. When the TV  10  changes in operation state, the operation state storage unit  122  stores a start time of the operation state and information showing the operation state. The operation state storage unit  122  also stores a flag showing whether or not the state change to the operation state is caused by the operation mode switching timer  101 . The operation state storage unit  122  further stores information that the operation state continues, in an operation duration time storage unit at predetermined time intervals. 
     The DVD recorder  20  is an apparatus that records a broadcast signal received via an antenna (not shown), and outputs a recorded video and audio signal via a HDMI cable. As shown in  FIG. 3 , the DVD recorder  20  includes an operation mode switching timer  201 , an electricity consumption amount storage unit  202 , a saved electricity consumption amount storage unit  203 , an electricity consumption storage unit  204 , a remote control reception unit  205 , an active source state storage unit  208 , a microcomputer  210 , a CEC communication unit  211 , a decoding unit  212 , a TMDS output unit  213 , a HDMI output unit  214 , a TV power state determination unit  216 , a recording timer  217 , an IP communication unit  218 , a recording unit  219 , a tuner  220 , an operation function setting storage unit  221 , and an operation state storage unit  222 . 
     The operation mode switching timer  201  includes a timer and an operation mode switching time storage unit. The operation mode switching timer  201  stores the time  1  to switch to the operation mode  1  and the time  2  to switch to the operation mode  2 , via the microcomputer  210 . When the time  1  or the time  2  is reached, the operation mode switching timer  201  notifies the microcomputer  210  that the corresponding set time is reached. 
     The electricity consumption amount storage unit  202  includes a current-day storage unit that temporarily stores an amount of electricity consumption of the current day, and a log recording unit that stores an amount of electricity consumption of the past fixed time period. Note that the log recording unit in the electricity consumption amount storage unit  202  is composed of a nonvolatile storage device. 
     The saved electricity consumption amount storage unit  203  includes a current-day storage unit that temporarily stores an amount of saved electricity consumption of the current day, and a log recording unit that stores an amount of saved electricity consumption of the past fixed time period. Note that the log recording unit in the saved electricity consumption amount storage unit  203  is composed of a nonvolatile storage device. 
     The electricity consumption storage unit  204  stores electricity consumption in each of a plurality of operation states of the DVD recorder  20 . 
     The remote control reception unit  205  receives a signal transmitted from the remote control  40  (not shown) corresponding to the DVD recorder  20 , and notifies the microcomputer  210  of the signal. Here, as mentioned earlier, the remote control  40  includes the plurality of buttons such as the power button, the menu display button, and the up, down, left, and right buttons, and the remote control signal transmission unit, as the input unit. 
     The active source state storage unit  208  stores information that the DVD recorder  20  is an active source, when the CEC communication unit  211  transmits an &lt;Active Source&gt; command. When the CEC communication unit  211  receives an &lt;Active Source&gt; command from another apparatus, on the other hand, the active source state storage unit  208  deletes the information that the DVD recorder  20  is in an active source state. 
     The microcomputer  210  is a device that executes a program. The microcomputer  210  receives a notification from any of the operation mode switching timer  201 , the remote control reception unit  205 , the CEC communication unit  211 , the TV power state determination unit  216 , and the recording timer  217 . Upon receiving the notification, the microcomputer  210  reads or writes information in each storage unit such as the electricity consumption storage unit  204 , the electricity consumption amount storage unit  202 , the saved electricity consumption amount storage unit  203 , the active source state storage unit  208 , and the operation function setting storage unit  221 , and also controls the CEC communication unit  211 , the decoding unit  212 , the IP communication unit  218 , the recording unit  219 , the tuner  220 , and the like. The microcomputer  210  also controls other various functions of the DVD recorder  20  not shown. 
     For example, the microcomputer  210  controls an IP communication unit (IP communication function) that communicates with another apparatus, and a LED clock display unit (LED clock display function) that displays a current time, received channel information, and the like. The microcomputer  210  also controls the recording unit  219  (recording function) that records a broadcast signal (containing video and audio data) outputted from the tuner. The microcomputer  210  can perform power ON/OFF control on each of these components individually. 
     The CEC communication unit  211  is an example of a device that transmits and receives a control command via the communication network. The CEC communication unit  211  performs transmission and reception of a CEC command. 
     Note that the communication network for transmitting and receiving the control command is not limited to CEC, and a wired or wireless network of IP or the like may instead be used. 
     The decoding unit  212  appropriately decodes video and audio data received from the tuner  220  or the recording unit  219 , and outputs the decoded video data and audio data to the TMDS output unit  213 . 
     The TMDS output unit  213  outputs the video data and the audio data via a TMDS signal  214 _ 3  in the HDMI output unit  214 , as a TMDS data signal. 
     The HDMI output unit  214  outputs the TMDS data received from the TMDS output unit  213 , using the TMDS signal  214 _ 3 . 
     The TV power state determination unit  216  receives a CEC command transmitted from the TV  10  via the CEC communication unit  211 , and determines whether the TV  10  is powered ON or OFF by querying a power state of the TV  10 . The TV power state determination unit  216  notifies the microcomputer  210  of a result of the determination. 
     The recording timer  217  is a timer for starting programmed recording of a broadcast. When a set time is reached, the recording timer  217  notifies the recording unit  219  and the microcomputer  210  of the recording start. 
     The IP communication unit  218  is an example of a function of the DVD recorder  20 , and performs information transmission and reception with a connected apparatus (not shown) by IP communication. 
     The recording unit  219  is a device that records a broadcast signal outputted from the tuner  220 , in a storage device such as a hard disk. 
     The tuner  220  outputs a broadcast signal received via an antenna (not shown), to the recording unit  219  or the decoding unit  212 . 
     The operation function setting storage unit  221  stores a table showing correspondence between various operation states and various functions of the DVD recorder  20 , as shown in  FIG. 5A . 
     Note that the functions of the DVD recorder  20  shown in  FIG. 5A  are merely an example, and the present invention is not limited to these functions. All functions of the DVD recorder  20  are associated with operation states. 
     The operation state storage unit  222  is a storage device. When the DVD recorder  20  changes in operation state, the operation state storage unit  222  stores a start time of the operation state and information showing the operation state. The operation state storage unit  222  also stores a flag showing whether or not the state change to the operation state is caused by the operation mode switching timer  201 . The operation state storage unit  222  further stores information that the operation state continues, in an operation duration time storage unit at predetermined time intervals. 
     The set-top box  30  is an apparatus that decodes a broadcast signal received via a broadcast signal cable (not shown), and outputs a video and audio signal via a HDMI cable. 
     As shown in  FIG. 4 , the set-top box  30  includes an operation mode switching timer  301 , an electricity consumption amount storage unit  302 , a saved electricity consumption amount storage unit  303 , an electricity consumption storage unit  304 , a remote control reception unit  305 , an active source state storage unit  308 , a microcomputer  310 , a CEC communication unit  311 , a decoding unit  312 , a TMDS output unit  313 , a HDMI output unit  314 , a TV power state determination unit  316 , a tuner  320 , an operation function setting storage unit  321 , and an operation state storage unit  322 . 
     The operation mode switching timer  301  includes a timer and an operation mode switching time storage unit. The operation mode switching timer  301  stores the time  1  to switch to the operation mode  1  and the time  2  to switch to the operation mode  2 , via the microcomputer  310 . When the time  1  or the time  2  is reached, the operation mode switching timer  301  notifies the microcomputer  310  that the corresponding set time is reached. 
     The electricity consumption amount storage unit  302  includes a current-day storage unit that temporarily stores an amount of electricity consumption of the current day, and a log recording unit that stores an amount of electricity consumption of the past fixed time period. Note that the log recording unit in the electricity consumption amount storage unit  302  is composed of a nonvolatile storage device. 
     The saved electricity consumption amount storage unit  303  includes a current-day storage unit that temporarily stores an amount of saved electricity consumption of the current day, and a log recording unit that stores an amount of saved electricity consumption of the past fixed time period. Note that the log recording unit in the saved electricity consumption amount storage unit  303  is composed of a nonvolatile storage device. 
     The electricity consumption storage unit  304  stores electricity consumption in each of a plurality of operation states of the set-top box  30 . 
     The remote control reception unit  305  receives a signal transmitted from the remote control  40  (not shown) corresponding to the DVD recorder  20 , and notifies the microcomputer  310  of the signal. Here, as mentioned earlier, the remote control  40  includes the plurality of buttons such as the power button, the menu display button, and the up, down, left, and right buttons, and the remote control signal transmission unit, as the input unit. 
     The active source state storage unit  308  stores information that the set-top box  30  is an active source, when the CEC communication unit  311  transmits an &lt;Active Source&gt; command. When the CEC communication unit  311  receives an &lt;Active Source&gt; command from another apparatus, on the other hand, the active source state storage unit  308  deletes the information that the set-top box  30  is in an active source state. 
     The microcomputer  310  is a device that executes a program. The microcomputer  310  receives a notification from any of the operation mode switching timer  301 , the remote control reception unit  305 , the CEC communication unit  311 , and the TV power state determination unit  316 . Upon receiving the notification, the microcomputer  310  reads or writes information in each storage unit such as the electricity consumption storage unit  304 , the electricity consumption amount storage unit  302 , the saved electricity consumption amount storage unit  303 , the active source state storage unit  308 , and the operation function setting storage unit  321 , and also controls the CEC communication unit  311 , the decoding unit  312 , the tuner  320 , and the like. The microcomputer  310  also controls various functions of the set-top box  30  not shown. 
     The CEC communication unit  311  is an example of a device that transmits and receives a control command via the communication network. The CEC communication unit  311  performs transmission and reception of a CEC command. 
     Note that the communication network for transmitting and receiving the control command is not limited to CEC, and a wired or wireless network of IP or the like may instead be used. 
     The decoding unit  312  appropriately decodes video and audio data received from the tuner  320 , and outputs the decoded video data and audio data to the TMDS output unit  313 . 
     The TMDS output unit  313  outputs the video data and the audio data via a TMDS signal  314 _ 3  in the HDMI output unit  314 , as a TMDS data signal. 
     The HDMI output unit  314  outputs the TMDS data received from the TMDS output unit  313 , using the TMDS signal  314 _ 3 . 
     The TV power state determination unit  316  receives a CEC command transmitted from the TV  10  via the CEC communication unit  311 , and determines whether the TV  10  is powered ON or OFF by querying a power state of the TV  10 . The TV power state determination unit  316  notifies the microcomputer  310  of a result of the determination. 
     The tuner  320  outputs a broadcast signal received via an antenna (not shown), to the recording unit  219  or the decoding unit  212 . 
     The operation state storage unit  322  is a storage device. When the set-top box  30  changes in operation state, the operation state storage unit  322  stores a start time of the operation state and information showing the operation state. 
     The operation state storage unit  322  also stores a flag showing whether or not the state change to the operation state is caused by the operation mode switching timer  301 . The operation state storage unit  322  further stores information that the operation state continues, in an operation duration time storage unit at predetermined time intervals. 
     The operation function setting storage unit  321  stores a table showing correspondence between various operation states and various functions of the set-top box  30 , as shown in  FIG. 5B . 
     Note that the functions of the set-top box  30  shown in  FIG. 5B  are merely an example, and the present invention is not limited to these functions, so long as all functions of the set-top box are associated with operation states. 
     &lt;Operation&gt; 
     (Setting of Operation Mode and Operational Function Combination by the User) 
     The TV  10 , the DVD recorder  20 , and the set-top box  30  connected via the communication network store an operation mode and function correspondence table showing a function that is operational in each operation mode, respectively in the operation function setting storage units  121 ,  221 , and  321 . 
       FIGS. 5A ,  5 B, and  5 C respectively show an example of the operation mode and function correspondence table in the DVD recorder  20 , the set-top box  30 , and the TV  10 . In  FIGS. 5A ,  5 B, and  5 C, each of the DVD recorder  20 , the set-top box  30 , and the TV  10  has a plurality of operation modes, in each of which a function is energized so as to be operational or is not energized so as to be non-operational. 
     For example, in the DVD recorder  20 , when the operation mode of the DVD recorder  20  is a power-OFF operation mode  2  and also the TV power state determination unit  216  determines that the TV  10  is powered OFF, the recording function is operational but the IP communication function, the LED clock display function, and a HDMI video and audio output function are non-operational, as shown in  FIG. 5A . 
     Moreover, the DVD recorder  20  in a power-OFF state has at least a power-OFF operation mode  1  and the power-OFF operation mode  2  that differ in electricity consumption, as shown in  FIG. 5A . That is, the DVD recorder  20  has, for example, the power-OFF operation mode  1  and the power-OFF operation mode  2 . The power-OFF operation mode  1  is a state in which the DVD recorder  20  is in a power-OFF state but a part of the DVD recorder  20  is supplied with power, as in the case where the recording function and a main microcomputer function including the IP communication function and the LED clock display function are energized while the HDMI video and audio output function is not energized. The power-OFF operation mode  2  is a state in which the DVD recorder  20  is in a power-OFF state and fewer functions are operational than in the power-OFF operation mode  1 , as in the case where only the recording function is energized while the HDMI video and audio output function and the main microcomputer function are not energized. Thus, fewer functions are energized in the power-OFF operation mode  2  than in the power-OFF operation mode  1 , and so the power-OFF operation mode  2  has lower electricity consumption than the power-OFF operation mode  1 . 
     The DVD recorder  20  also has an operation mode  3  (full OFF mode) in which none of the HDMI video and audio output function, the recording function, and the main microcomputer function including the IP communication function and the LED clock display function is energized, as shown in  FIG. 5A . 
     Note that the same applies to the set-top box  30  and the TV  10 , and so their description is omitted here. 
     Though there is also a function such as a remote control reception function that is continuously operational regardless of the operation mode, such a function is not shown in this embodiment. Note that the functions shown in each of  FIGS. 5A ,  5 B, and  5 C are merely an example of a part of functions of the corresponding apparatus, and functions associated with operation modes are not limited to such. 
     The user can change the operation mode and function correspondence table by using the remote control  40  of the TV  10 , the DVD recorder  20 , and the set-top box  30 . 
       FIG. 6  shows an example of a menu for setting an operation mode and a function in the DVD recorder  20  in the first embodiment of the present invention. A menu  1600  is an example of an OSD (On Screen Display) menu display for changing the operation mode and function correspondence in the DVD recorder  20 . In  FIG. 6 , menu items  1602  to  1604  each show an operational function combination when switching to the operation mode, and a cursor  1601  shows a selected menu item. 
     When the user moves the cursor  1601  and selects a desired menu item through the input unit such as the remote control (not shown) of the DVD recorder  20 , the microcomputer  210  rewrites the operation mode and function correspondence table in the operation function setting storage unit  221  so as to have a value corresponding to the selected menu item. 
     The TV  10  and the set-top box  30  also have the same OSD menu display function. The user can rewrite the operation function setting storage units  121  and  321  by setting the respective apparatuses so that only a desired function is operational in each operation mode. 
     (Operation Mode Setting According to Time by the Timer in Each Apparatus) 
       FIG. 7  shows an example of an operation mode switching time setting method by an OSD menu display in the TV  10  in the first embodiment of the present invention. 
     First, the user designates the time  1  to start operation in the power-ON operation mode  1  and the power-OFF operation mode  1  and the time  2  to start operation in the power-ON operation mode  2  and the power-OFF operation mode  2 , through the input unit of the TV beforehand. 
     For example, the time  1  and the time  2  are set as follows. In a menu such as an OSD menu  2100  displayed by the video output unit  106  in the TV  10 , the user changes the start times of the operation mode  1  and the operation mode  2  to desired times by pressing buttons which constitute the input unit of the TV  10  such as the remote control  40 . 
     After the time  1  and the time  2  are determined by the user operation, the TV  10  transmits, from the CEC communication unit  111 , an operation mode switching time setting command having the user-designated time  1  and time  2  as a parameter, to the DVD recorder  20  and the set-top box  30  connected with the TV  10 . The TV also sets the time  1  and the time  2  in the operation mode switching timer  101 . 
     The DVD recorder  20  and the set-top box  30  receive the operation mode switching time setting command, and set the time  1  and the time  2  designated by the parameter in the received command, respectively in the operation mode switching timers  201  and  301 . 
     When the time  2  is reached, the operation mode switching timer  201  in the DVD recorder  20  notifies the microcomputer  210  that the time  2  is reached. 
     The microcomputer  210  receives the notification. When the operation mode of the DVD recorder  20  is the power-ON operation mode  1 , the microcomputer  210  switches the operation mode to the power-ON operation mode  2 . When the operation mode of the DVD recorder  20  is the power-OFF operation mode  1 , the microcomputer  210  switches the operation mode to the power-OFF operation mode  2 . The microcomputer  210  then starts operation. 
     Upon switching the operation mode, the DVD recorder  20  references the operation function setting storage unit  221  in the DVD recorder  20 . For a function that is set to be non-operational in the switched operation mode, the DVD recorder  20  ends a corresponding program or does not energize the function. For a function that is set to be operational in the switched operation mode, the DVD recorder  20  starts a corresponding program or energizes the function. 
     For example, in the case where the IP communication unit  218  in the DVD recorder  20  is set to be non-operational in the power-OFF operation mode  2 , the DVD recorder  20  ends a program of the IP communication unit  218  or does not energize the IP communication unit  218 . 
     Likewise, when the time  2  is reached, the operation mode switching timer  301  in the set-top box  30  notifies the microcomputer  310  that the time  2  is reached. 
     The microcomputer  310  receives the notification. When the operation mode of the set-top box  30  is the power-ON operation mode  1 , the microcomputer  310  switches the operation mode to the power-ON operation mode  2 . When the operation mode of the set-top box  30  is the power-OFF operation mode  1 , the microcomputer  310  switches the operation mode to the power-OFF operation mode  2 . The microcomputer  310  then starts operation. 
     Upon switching the operation mode, the set-top box  30  references the operation function setting storage unit  321  in the set-top box  30 , in the same manner as the DVD recorder  20 . For a function that is set to be non-operational in the switched operation mode, the set-top box  30  ends a corresponding program or does not energize the function. For a function that is set to be operational in the switched operation mode, the set-top box  30  starts a corresponding program or energizes the function. 
     Likewise, when the time  2  is reached, the operation mode switching timer  101  in the TV  10  notifies the microcomputer  110  that the time  2  is reached. 
     The microcomputer  110  receives the notification. When the operation mode of the TV  10  is the power-ON operation mode  1 , the microcomputer  110  switches the operation mode to the power-ON operation mode  2 . When the operation mode of the apparatus is the power-OFF operation mode  1 , the microcomputer  110  switches the operation mode to the power-OFF operation mode  2 . The microcomputer  110  then starts operation. 
     The TV  10 , the DVD recorder  20 , and the set-top box  30  also switch the operation mode according to the respective operation mode switching timers ( 101 ,  201 , and  301 ) when the time  1  is reached, in the same way as above. 
     When the time  1  is reached, the operation mode switching timer  201  in the DVD recorder  20  notifies the microcomputer  210  that the time  1  is reached. 
     The microcomputer  210  receives the notification. When the operation mode of the DVD recorder  20  is the power-ON operation mode  2 , the microcomputer  210  switches the operation mode to the power-ON operation mode  1 . When the operation mode of the apparatus is the power-OFF operation mode  2 , the microcomputer  210  switches the operation mode to the power-OFF operation mode  1 . The microcomputer  210  then starts operation. 
     Likewise, when the time  1  is reached, the operation mode switching timer  301  in the set-top box  30  notifies the microcomputer  310  that the time  1  is reached. 
     The microcomputer  310  receives the notification. When the operation mode of the DVD recorder  20  is the power-ON operation mode  2 , the microcomputer  310  switches the operation mode to the power-ON operation mode  1 . When the operation mode of the apparatus is the power-OFF operation mode  2 , the microcomputer  310  switches the operation mode to the power-OFF operation mode  1 . The microcomputer  310  then starts operation. 
     Likewise, when the time  1  is reached, the operation mode switching timer  101  in the TV  10  notifies the microcomputer  110  that the time  1  is reached. 
     The microcomputer  110  receives the notification. When the operation mode of the TV  10  is the power-ON operation mode  2 , the microcomputer  110  switches the operation mode to the power-ON operation mode  1 . When the operation mode of the TV  10  is the power-OFF operation mode  2 , the microcomputer  110  switches the operation mode to the power-OFF operation mode  1 . The microcomputer  110  then starts operation. 
     As described above, when the time to switch the operation mode of the DVD recorder  20  or the set-top box  30  is designated by the user in the TV  10 , the DVD recorder  20  or the set-top box  30  sets the designated time in the operation mode switching timer  201  or  301  on the basis of the control command transmitted from the TV  10 . When the designated time is reached, the DVD recorder  20  or the set-top box  30  switches to the operation mode designated by the user. Thus, the operation mode is switched according to the time by the timer in each apparatus. 
     Note that the operation mode switching time setting is not limited to the above two times. For instance, the operation mode may be designated according to the day and time, as shown in  FIG. 8 . Moreover, the number of operation modes is not limited to two, and three or more operation modes may be subject to switching. 
     In addition, the timing of switching the operation mode is not limited to a time of day, and may instead be an elapsed time. In this case, for example, when one operation mode continues for a predetermined elapsed time, the operation mode is switched to another operation mode upon the elapse of the time. 
     (Operation Mode Switching in Synchronization with Power ON/OFF) 
     The DVD recorder  20  and the set-top box  30  can also switch to the operation mode  1  or the operation mode  2  in synchronization with the operation of the TV  10 , without depending on the operation mode switching timers  201  and  301 . The following describes a process whereby the DVD recorder  20  and the set-top box  30  switch to the operation mode  1  or the operation mode  2  in synchronization with the power state of the TV  10 , without depending on the operation mode switching timers  201  and  301 . 
     The TV power state determination units  216  and  316  in the DVD recorder  20  and the set-top box  30  detect a change in power state of the TV  10  and determine the power state of the TV  10 , respectively via the CEC communication units  211  and  311 . 
     In order to determine the power state of the TV  10 , the TV power state determination units  216  and  316  transmit a &lt;Give Power Status&gt; command to query the power state of the TV  10  at regular time intervals. 
     The TV  10  receives the &lt;Give Power Status&gt; command, and transmits a &lt;Report Power Status&gt; command having a power-ON state or a power-OFF state as a parameter, to the apparatus transmitting the &lt;Give Power Status&gt; command. 
     By receiving the &lt;Report Power Status&gt; command at the regular time intervals, the TV power state determination units  216  and  316  can detect a change in power state of the TV  10  and determine the power state of the TV  10 . 
     In the case of transmitting a specific CEC command when the TV  10  is powered ON or when the TV  10  is powered OFF, the TV power state determination units  216  and  316  can determine whether the TV  10  is powered ON or OFF, upon receiving the specific CEC command. 
     For example, in the case of transmitting a &lt;Standby&gt; command when the TV  10  is powered OFF, the TV power state determination units  216  and  316  in the DVD recorder  20  and the set-top box  30  can determine that the TV  10  is powered OFF, upon receiving the &lt;Standby&gt; command from the TV  10 . 
     The following describes a processing flow when the user powers ON the TV  10  by pressing the power button (not shown) on the remote control  40  of the TV  10  or a cabinet of the TV  10 . 
     First, the TV power state determination units  216  and  316  in the DVD recorder  20  and the set-top box  30  detect that the TV  10  is powered ON, and notify the microcomputers  210  and  310  that the TV  10  is powered ON. 
     Upon detecting the power ON of the TV  10  through the notification, the microcomputers  210  and  310  in the DVD recorder  20  and the set-top box  30  switch the operation mode to the power-ON operation mode  1  or the power-OFF operation mode  1 , and start operation. 
     When the user powers OFF the TV  10  by pressing the power button (not shown) on the remote control  40  of the TV  10  or the cabinet of the TV  10  while the TV  10  is operating in a power-ON state, the TV  10  transmits a &lt;Standby&gt; command for powering OFF a connected apparatus. 
     The TV power state determination units  216  and  316  in the DVD recorder  20  and the set-top box  30  receive the &lt;Standby&gt; command, and determine that the TV  10  is powered OFF. The TV power state determination units  216  and  316  respectively notify the microcomputers  210  and  310  of a result of the determination. 
     The microcomputers  210  and  310  in the DVD recorder  20  and the set-top box  30  detect the power OFF of the TV  10  through the notification. Since the &lt;Standby&gt; command has been received, the microcomputers  210  and  310  switch the operation mode to the power-OFF operation mode  2  and start operation. 
     Thus, the DVD recorder  20  and the set-top box  30  can switch to the operation mode  1  or the operation mode  2 , without depending on the operation mode switching timers  201  and  301 . That is, the DVD recorder  20  and the set-top box  30  determine whether the TV  10  is powered ON or OFF, and switch the operation mode in synchronization with the power ON or OFF of the TV  10 . 
     Note that the method whereby the TV power state determination units  216  and  316  determine the power state of the TV  10  is not limited to the above method. As an example, the DVD recorder  20  and the set-top box  30  may detect that the TV  10  is powered OFF, by receiving a &lt;Report Power Status&gt; command having a power-OFF state of the TV  10  as a parameter. 
     (Powering OFF the DVD Recorder  20  and the Set-Top Box According to the User&#39;s Viewing Operation) 
     For example, suppose input selection for video and audio data viewed on the TV  10  is made from the DVD recorder  20  to the set-top box  30  while the DVD recorder  20  is in the operation mode  1  or the operation mode  2 . 
     When the user is viewing video and audio from the set-top box  30  on the TV  10 , video and audio data outputted from the DVD recorder  20  cannot be viewed on the TV  10 . In such a case, the DVD recorder  20  is powered OFF. The same applies to the set-top box  30 . In detail, when the input of the TV  10  is the DVD recorder  20 , the set-top box  30  is powered OFF because video and audio data outputted from the set-top box  30  cannot be viewed on the TV  10 . 
       FIG. 9  shows an example of a flow of CEC command transmission and reception when the DVD recorder  20  and the set-top box  30  operate according to the user&#39;s operation. The following describes a process whereby the DVD recorder  20  and the set-top box are powered OFF according to the user&#39;s viewing operation of the TV  10 , with reference to  FIG. 9 . 
     First, the user powers ON the TV  10  by operating the input unit of the TV  10  such as the remote control  40  (Step S 101 ). 
     After the TV  10  is powered ON, in the case of reproducing video and audio from the tuner  120  included in the TV  10 , the TV  10  broadcasts an &lt;Active Source&gt; command to the DVD recorder  20  and the set-top box  30 . At this time, both the DVD recorder  20  and the set-top box  30  are not in a power-ON state, so that the DVD recorder and the set-top box  30  perform no operation in response to the &lt;Active Source&gt; command (Steps S 102 , S 103 ). 
     However, the TV power state determination units  216  and  316  in the DVD recorder  20  and the set-top box  30  determine that the TV  10  is powered ON by detecting a CEC command transmitted when the TV  10  is powered ON, and notify the microcomputers  210  and  310  that the TV  10  is powered ON. 
     Upon receiving the notification, the microcomputer  210  references the operation function setting storage unit  221 . When the apparatus is in the operation mode  1 , the microcomputer  210  activates a function that is operational in a power-ON state of the TV in the power-OFF operation mode  1 . When the apparatus is in the operation mode  2 , on the other hand, the microcomputer  210  activates a function that is operational in a power-ON state of the TV  10  in the power-OFF operation mode  2 . 
     Likewise, the microcomputer  310  in the set-top box  30  references the operation function setting storage unit  321 . When the apparatus is in the operation mode  1 , the microcomputer  310  activates a function that is operational in a power-ON state of the TV  10  in the power-OFF operation mode  1 . When the apparatus is in the operation mode  2 , on the other hand, the microcomputer  310  activates a function that is operational in a power-ON state of the TV in the power-OFF operation mode  2 . 
     Next, to start viewing the set-top box  30 , the user performs selection by selecting an OSD menu displayed on the TV  10  or pressing a button on the remote control  40  of the TV  10  (Step S 104 ). 
     The TV  10  responsively transmits a power-ON command to the set-top box  30  (Step S 105 ). 
     The set-top box  30  receives the power-ON command, transitions to a power-ON state in the operation mode  1  or the operation mode  2 , and starts outputting video and audio (Step S 106 ). When starting the video and audio output, the set-top box  30  transmits an &lt;Active Source&gt; command to the TV  10  and the DVD recorder  20 , and stores information that the set-top box  30  is in an active source state, in the active source state storage unit  308  in the set-top box  30 . 
     Next, to start viewing the DVD recorder  20 , the user performs selection by selecting a menu displayed on the TV  10  or pressing a button on the remote control  40  of the TV  10  (Step S 107 ). 
     The TV  10  responsively transmits a power-ON command to the DVD recorder  20  (Step S 108 ). 
     The DVD recorder  20  receives the power-ON command, and references the operation function setting storage unit  221 . The DVD recorder  20  transitions to a power-ON state by operating a function corresponding to the current operation mode. The DVD recorder  20  further starts outputting video and audio. When starting the video and audio output, the DVD recorder  20  transmits an &lt;Active Source&gt; command to the TV  10  and the set-top box  30  (Step S 109 ), and also stores information that the DVD recorder  20  is in an active source state, in the active source state storage unit  208 . 
     Upon receiving the &lt;Active Source&gt; command transmitted in Step S 109 , the set-top box  30  determines that another apparatus is in an active source state. The set-top box  30  accordingly deletes the information that the set-top box  30  is in an active source state from the active source state storage unit  308 , and transitions to a power-OFF state (Step S 110 ). 
     Here, in Step S 110 , the microcomputer  310  in the set-top box  30  references the operation function setting storage unit  321 . When the apparatus (the set-top box  30 ) is in the operation mode  1 , the microcomputer  310  ends an unnecessary function so as to operate only a function that is operational in a power-ON state of the TV  10  in the power-OFF operation mode  1 . When the apparatus is in the operation mode  2 , the microcomputer  310  ends an unnecessary function so as to operate only a function that is operational in a power-ON state of the TV  10  in the power-OFF operation mode  2 . 
     Likewise, upon receiving an &lt;Active Source&gt; command from an apparatus other than the DVD recorder  20 , the DVD recorder determines that another apparatus is in an active source state. The DVD recorder  20  accordingly deletes the information that the DVD recorder  20  is in an active source state from the active source state storage unit  208 , and transitions to a power-OFF state (Step S 114 ). 
     In Step S 114 , the microcomputer  210  in the DVD recorder  20  references the operation function setting storage unit  221 . When the apparatus (the DVD recorder  20 ) is in the operation mode  1 , the microcomputer  210  ends an unnecessary function so as to operate only a function that is operational in a power-ON state of the TV  10  in the power-OFF operation mode  1 . When the apparatus is in the operation mode  2 , the microcomputer  210  ends an unnecessary function so as to operate only a function that is operational in a power-ON state of the TV  10  in the power-OFF operation mode  2 . 
     When the user presses an input selection button of the TV  10 , the TV  10  transmits a &lt;Set Stream Path&gt; command having, as a parameter, a PA of an apparatus connected to a designated input. 
     In the case, the DVD recorder  20  or the set-top box  30  is powered ON and transmits an &lt;Active Source&gt; command, when the PA shown by the parameter in the &lt;Set Stream Path&gt; command is the same as a PA of the apparatus. The DVD recorder  20  or the set-top box  30  then starts outputting video and audio data, and also stores information that the apparatus is in an active source state, in the active source state storage unit  208  or  308 . 
     Note that, after the DVD recorder  20  or the set-top box is powered OFF as a result of receiving an &lt;Active Source&gt; command, if no operation is performed on the apparatus for a predetermined time period through any of the remote control  40 , a button on a cabinet of the set-top box  30 , CEC, and the like, it can be assumed that the user&#39;s operation on the apparatus does not occur. In such a case, the DVD recorder  20  or the set-top box  30  references the operation function setting storage unit  221  or  321 , and transitions to a power-OFF state where an unnecessary function is further ended by operating only a function that is operational in a power-OFF state of the TV  10  in the operation mode  1  or the operation mode  2 . This is described below, with reference to  FIG. 9 . 
     Suppose, after Step S 114 , to view a broadcast by the tuner  120  in the TV  10 , the user performs selection by selecting an OSD menu displayed on the TV  10  or pressing a button on the remote control  40  of the TV  10 , as shown in  FIG. 9  (Step S 115 ). 
     In this case, the TV  10  transmits an &lt;Active Source&gt; command to the DVD recorder  20  and the set-top box  30  (Steps S 116 , S 117 ). 
     Upon receiving the &lt;Active Source&gt; command transmitted in Step S 116 , the set-top box  30  determines that another apparatus is in an active source state. The set-top box  30  accordingly deletes the information that the set-top box  30  is in an active source state from the active source state storage unit  308 , and transitions to a power-OFF state (power-OFF operation mode  1 ). 
     Here, the DVD recorder  20  also receives the &lt;Active Source&gt; command transmitted in Step S 117 , but performs no operation in response to this command because the DVD recorder  20  has already transitioned to a power-OFF state (power-OFF operation mode  1 ) in Step S 114 . 
     In the case where, while the user continues viewing the broadcast by the tuner  120  in the TV  10 , no operation is performed on the DVD recorder  20  and the set-top box  30  for the predetermined time period after the DVD recorder  20  and the set-top box  30  are powered OFF, the DVD recorder  20  and the set-top box  30  switch the operation mode in a power-OFF state from the operation mode  1  (power-OFF operation mode  1 ) to the operation mode  2  (power-OFF operation mode  2 ). 
     Here, the DVD recorder  20  and the set-top box  30  in a power-OFF state have at least two operation modes that differ in electricity consumption, namely, the power-OFF operation mode  1  and the power-OFF operation mode  2 . As shown in  FIG. 5 , the power-OFF operation mode  2  has fewer operational functions than the power-OFF operation mode  1 , and so has lower electricity consumption than the power-OFF operation mode  1 . 
     Therefore, in the DVD recorder  20  and the set-top box  30 , the number of operational functions when the TV  10  is powered OFF can be reduced as compared with the number of operational functions when the TV  10  is powered ON. Moreover, in the case where no operation is performed on the DVD recorder  20  and the set-top box  30  for the predetermined time period in a power-OFF state, the DVD recorder  20  and the set-top box  30  can be switched to a power-OFF state of lower electricity consumption, on an assumption that there is no need to immediately power ON the DVD recorder  20  and the set-top box  30 . This further contributes to lower electricity consumption, so that a reduction in electricity consumption can be achieved. 
     Note that, in the case where there is no operation even when the predetermined time period has elapsed as mentioned above, the TV  10  which serves as a master apparatus for the DVD recorder  20  and the set-top box  30  may make the assumption that there is no need to immediately power ON. For example, when there is no operation on the TV  10  for the predetermined time period while the user continues viewing the broadcast by the tuner  120  in the TV  10 , the TV  10  transmits a control command for controlling another apparatus, to the DVD recorder  20  and the set-top box  30 . In this case, the DVD recorder  20  and the set-top box  30  switch to a power-OFF state of lower electricity consumption, on the basis of the received control command. 
     Moreover, the DVD recorder  20  and the set-top box  30  do not need to be immediately powered OFF upon receiving the &lt;Active Source&gt; command, and may instead be powered OFF when no operation is performed for a fixed time period after the reception. 
     In the above way, the DVD recorder  20  and the set-top box  30  can each be powered OFF according to the user&#39;s viewing operation. By ending an unnecessary function when the user is not viewing the apparatus, it is possible to reduce electricity consumption. 
     (Electricity Consumption Amount Recording) 
     The TV  10 , the DVD recorder  20 , and the set-top box  30  each record an amount of electricity consumption, i.e., an amount of electrical power consumed in the apparatus, and an amount of saved electricity consumption achieved as a result of a change in operation state caused by the operation mode switching timer. 
     In addition, in each of the TV  10 , the DVD recorder  20 , and the set-top box  30 , a correspondence table of each operation state and electricity consumption of the apparatus in the operation state is stored in the electricity consumption storage unit ( 104 ,  204 , and  304 ) beforehand. Note that, when there is no significant difference in electricity consumption between operational function combinations, such combinations may be shown together as one state. 
     The following describes a process whereby the TV  10  obtains an amount of electricity consumption and an amount of saved electricity consumption, taking the DVD recorder  20  as an example. 
       FIG. 10  is a diagram showing an example of a correspondence table of each operation state and electricity consumption in the DVD recorder  20 . In  FIG. 10 , electricity consumption is 40 W in an operation state E 1 , 10 W in an operation state E 2 , and 0.5 W in an operation state E 3  in the DVD recorder  20 . 
     When the DVD recorder  20  changes in operation state as a result of the user&#39;s operation of the input unit (not shown), the CEC command reception, or the operation of the timer in the DVD recorder such as the recording timer  217  or the operation mode switching timer  201 , the DVD recorder  20  stores a start time of the operation state and information showing the operation state in the operation state storage unit  222 . 
     In the case where the change of the operation state is caused by the operation mode switching timer  201 , the DVD recorder also stores a flag showing that the state change is caused by the operation mode switching timer  201 , in the operation state storage unit  222 . 
     After this, when the DVD recorder  20  changes in operation state, the DVD recorder  20  calculates an amount of electricity consumption and an amount of saved electricity consumption in the operation state before the change. This is described in detail below. 
     First, the DVD recorder  20  references the operation state storage unit  222 , and calculates a difference between the start time of the operation state and the current time as a duration of the operation state. 
     Next, the DVD recorder  20  references the operation state before the change in the operation state storage unit  222 , and obtains electricity consumption in the operation state with reference to the electricity consumption storage unit  204 . 
     The DVD recorder  20  then calculates a product of the duration of the operation state and the electricity consumption in the operation state, as the amount of electricity consumption in the operation state. The DVD recorder  20  stores the amount of electricity consumption, by adding the amount of electricity consumption to a value stored in the current-day storage unit in the electricity consumption amount storage unit  202 . The DVD recorder also stores the current time and the operation state after the change, in the operation state storage unit  222 . 
     In the same manner, when the DVD recorder  20  changes in operation state again, an amount of electricity consumption is calculated from a product of a duration of the operation state and electricity consumption, and the amount of electricity consumption is stored by being added to the value stored in the current-day storage unit in the electricity consumption amount storage unit  202 . The above series of operations is repeated in this way. 
     Moreover, the DVD recorder  20  references the operation state storage unit  222  and, when the state change is caused by the operation mode switching timer  201 , calculates the amount of saved electricity consumption. The amount of saved electricity consumption is calculated by the following procedure. 
     The DVD recorder  20  calculates a difference between the electricity consumption in the operation state stored in the operation state storage unit  222  and electricity consumption in a normal state. The DVD recorder  20  then calculates a product of the electricity consumption difference and the duration of the operation state, as the amount of saved electricity consumption. 
     Here, the electricity consumption in the normal state is electricity consumption in an operation state in the case of not setting the operation mode switching timer  201 . Accordingly, the amount of saved electricity consumption indicates an amount of electricity consumption reduced by the operation of the operation mode switching timer  201 . The amount of saved electricity consumption is stored by being added to a value in the current-day storage unit in the saved electricity consumption amount storage unit  203 , in the same way as the amount of electricity consumption. 
     Furthermore, the electricity consumption amount storage unit  202  stores a pair of a value corresponding to the current day and a recording date and time in the log recording unit in the electricity consumption amount storage unit  202 , at regular time intervals such as 24-hour intervals. The electricity consumption amount storage unit  202  also resets the value in the current-day storage unit in the electricity consumption amount storage unit  202  to 0. 
     Likewise, the saved electricity consumption amount storage unit  203  stores a pair of a value corresponding to the current day and a recording date and time in the log recording unit in the saved electricity consumption amount storage unit  203 , at regular time intervals such as 24-hour intervals. The saved electricity consumption amount storage unit  203  also resets the value in the current-day storage unit in the saved electricity consumption amount storage unit  203  to 0. 
     Note that the time intervals of recording a log of the amount of electricity consumption and the amount of saved electricity consumption are not limited to 24-hour intervals, so long as they are regular time intervals. 
     Each log recording unit records, for example, a log corresponding to 30 days, and deletes the log in order of occurrence when 30 days are exceeded. 
     In addition to the above-mentioned operations, the DVD recorder  20  stores, together with the current time, information that there is no change in operation state of the DVD recorder  20 , in the operation duration time storage unit in the operation state storage unit  222  at predetermined time intervals. 
     There is the case where power supply to the DVD recorder  20  is stopped by, for example, the user removing a power cable of the DVD recorder  20  from a receptacle. When this occurs, upon receiving power supply again, the DVD recorder  20  starts operation, and also obtains the operation state, the start time of the operation state, and the duration time of the operation state with reference to the operation state storage unit  222 . The DVD recorder calculates a difference between the start time of the operation state and the duration time of the operation state, and stores a product of the difference and the electricity consumption in the operation state by adding the product to the value in the current-day storage unit in the electricity consumption amount storage unit  202 . 
       FIG. 11  shows an example of changes in operation and electricity consumption of the DVD recorder  20 . The following describes an example of storing the amount of electricity consumption and the amount of saved electricity consumption, with reference to  FIG. 1 . In  FIG. 11 , a horizontal axis represents a time, and a vertical axis represents electricity consumption at the time. 
     First, when the DVD recorder  20  is connected to the receptacle (not shown) and starts operation in the operation state E 3  at 0 o&#39;clock, information that the operation state E 3  starts at 0 o&#39;clock is stored in the operation state storage unit  222 . 
     Following this, the user powers ON the DVD recorder  20  at 1 o&#39;clock (“power ON A” in  FIG. 11 ). Since a duration of the operation state E 3  is 1 hour from 0 o&#39;clock to 1 o&#39;clock, 0.5 W (the electricity consumption of the operation state E 3 )×1 hour=0.5 Wh is stored in the current-day storage unit in the electricity consumption amount storage unit  202 . Meanwhile, as a result of changing to the operation state E 1 , information that the operation state E 1  starts at 1 o&#39;clock is stored in the operation state storage unit  222 . 
     Next, the user powers OFF the DVD recorder  20  at 2 o&#39;clock (“power OFF” in  FIG. 11 ). Since a duration of the operation state E 1  is 1 hour from 1 o&#39;clock to 2 o&#39;clock, 40 W (the electricity consumption of the operation state E 1 )×1 hour=40 Wh is stored in the current-day storage unit in the electricity consumption amount storage unit  202 . This yields 40.5 Wh as the amount of electricity consumption of the current day. Meanwhile, information that the operation state E 2  starts at 2 o&#39;clock is stored in the operation state storage unit  222 . 
     Next, the operation mode switching timer  201  operates to change to the operation state E 3  at 3 o&#39;clock (“operation state switching timer” in  FIG. 11 ). Since a duration of the operation state E 2  is 1 hour from 2 o&#39;clock to 3 o&#39;clock, 10 W (the electricity consumption of the operation state E 2 )×1 hour=10 Wh is stored in the current-day storage unit in the electricity consumption amount storage unit  202 . This yields 50.5 Wh as the amount of electricity consumption of the current day. Meanwhile, information that the operation state E 3  starts at 3 o&#39;clock and the change of the operation state is caused by the operation mode switching timer  201  is stored in the operation state storage unit  222 . 
     After this, the user powers ON the DVD recorder  20  at 6 o&#39;clock, as a result of which the operation state changes to the operation state E 1 . Since a duration of the operation state E 3  is from 3 o&#39;clock to 6 o&#39;clock, 0.5 W (the electricity consumption of the operation state E 3 )×3 hours=1.5 Wh is stored in the current-day storage unit in the electricity consumption amount storage unit  202 . This yields 52 Wh as the amount of electricity consumption of the current day. 
     Moreover, since the change to the operation state E 3  is caused by the operation mode switching timer  201 , the amount of saved electricity consumption is calculated. The DVD recorder  20  is changed to the operation state E 3  by the operation mode switching timer  201 , instead of the operation state E 2  which is a normal operation state when the user powers OFF the DVD recorder  20 . Accordingly, 9.5 W (the difference between the electricity consumption of the operation state E 2  and the electricity consumption of the operation state E 3 )×3 hours=28.5 Wh is stored in the current-day storage unit in the saved electricity consumption amount storage unit  203 . Meanwhile, information that the operation state E 1  starts at 6 o&#39;clock is stored in the operation state storage unit  222 . 
     Thus, the DVD recorder  20  can calculate the amount of electricity consumption and the amount of saved electricity consumption. 
     In the same manner, the TV  10  and the set-top box  30  can obtain the amount of electricity consumption and the amount of saved electricity consumption, respectively using the operation state storage units  122  and  322 , the electricity consumption storage units  104  and  304 , the electricity consumption amount storage units  102  and  302 , and the saved electricity consumption amount storage units  103  and  303 . 
     (Electricity Consumption Amount Display by the TV  10 ) 
     The following describes the case where the user operates the remote control  40  of the TV  10  or a menu of the TV  10  to display an amount of electricity consumption and an amount of saved electricity consumption. 
     First, the TV  10  transmits an electricity consumption amount request command requesting electricity consumption amount information and a saved electricity consumption amount request command requesting saved electricity consumption amount information, to a connected apparatus. 
     The DVD recorder  20  and the set-top box  30  receive the electricity consumption amount request command. The DVD recorder  20  and the set-top box  30  respectively reference information in the log recording units in the electricity consumption amount storage units  202  and  302 , and transmit an electricity consumption amount notification command having, as a parameter, a pair of an amount of electricity consumption and a recording date and time, to the TV  10 . 
     The DVD recorder  20  and the set-top box  30  also receive the saved electricity consumption amount request command. The DVD recorder  20  and the set-top box  30  respectively reference information in the log recording units in the saved electricity consumption amount storage units  203  and  303 , and transmit a saved electricity consumption amount notification command having, as a parameter, a pair of an amount of saved electricity consumption and a recording date and time, to the TV  10 . 
     Having received the electricity consumption amount notification command from each of the DVD recorder  20  and the set-top box  30 , the TV  10  calculates a total amount of electricity consumption of the apparatuses, and displays the amount of electricity consumption on a daily basis. 
       FIG. 12  shows an example of displaying, on the TV  10 , an operation state of each apparatus and a total amount of electricity consumption of the AV system in the first embodiment of the present invention. 
     For example, as shown by an OSD display  2002  in  FIG. 12 , an amount of electricity consumption from 30 days ago up to 1 day ago can be displayed where a horizontal axis represents a time and a vertical axis represents an amount of electricity consumption. 
     Likewise, having received the saved electricity consumption amount notification command from each of the DVD recorder  20  and the set-top box  30 , the TV  10  calculates a total amount of saved electricity consumption on a daily basis and displays it in the video output unit  106 . Here, values stored in the electricity consumption amount storage unit  102  and the saved electricity consumption amount storage unit  103  in the TV  10  may be added respectively to the displayed amount of electricity consumption and amount of saved electricity consumption. 
     Note that the display of each of the amount of electricity consumption and the amount of saved electricity consumption may be performed by displaying the number of icons proportional to the amount. 
     Moreover, the amount of electricity consumption and the amount of saved electricity consumption may be OSD-displayed when the user powers ON the TV  10  and the TV  10  starts video output. 
     Thus, the amount of electricity consumption and the amount of saved electricity consumption of the TV  10 , the DVD recorder  20 , and the set-top box  30  can be displayed to the user. 
     As described above, according to the first embodiment, a master apparatus (the TV  10  in this embodiment) transmits a control command for controlling an apparatus other than the master apparatus to the other apparatus, thereby enabling the other apparatus to switch its operation state on the basis of the received control command. This contributes to higher electricity consumption efficiency in the AV system. 
     Therefore, in the AV system where a plurality of apparatuses that each have a plurality of operation states of different electricity consumption are connected via a communication network such as HDMI, the plurality of operation states in the plurality of apparatuses can be controlled so as to improve electricity consumption efficiency in the AV system. 
     Second Embodiment 
     A second embodiment has the same structures and functions as the first embodiment described above, and so the same structures as the first embodiment are given the same reference numerals in the drawings and their description is omitted. 
     &lt;Structure&gt; 
       FIG. 13  is a diagram schematically showing a structure of an AV system in the second embodiment.  FIG. 14  is a functional block diagram of a TV  50  in the second embodiment.  FIG. 15  is a functional block diagram of a DVD recorder  60  in the second embodiment.  FIG. 16  is a functional block diagram of a set-top box  70  in the second embodiment. Note that, in  FIGS. 14 ,  15 , and  16 , the same components as those in  FIGS. 2 ,  3 , and  4  are given the same reference numerals and their detailed description is omitted here. 
     The TV  50  in the second embodiment is an example of the first apparatus according to the present invention, and the DVD recorder  60  and the set-top box  70  in the second embodiment are each an example of the second apparatus according to the present invention. 
     As shown in  FIG. 13 , the AV system in the second embodiment includes the TV  50 , the DVD recorder  60 , and the set-top box  70 . The AV system also includes, for example, the remote control  40 . 
     In the AV system, the DVD recorder  60  and the set-top box  70  are connected to the TV  50  via HDMI cables. CEC lines in in HDMI are connected in a CEC communication unit  511  in the TV  50 . The TV  50 , the DVD recorder  60 , and the set-top box  70  are capable of performing transmission and reception of a CEC command as a control command with each other. 
     The TV  50  is an apparatus that outputs video and audio outputted from an apparatus connected via a HDMI cable, and a broadcast signal received via an antenna (not shown). 
     The TV  50  includes an operation mode switching timer  501 , an electricity consumption amount storage unit  502 , a saved electricity consumption amount storage unit  503 , the electricity consumption storage unit  104 , the remote control reception unit  105 , the video output unit  106 , the audio output unit  107 , the active source apparatus storage unit  108 , the connected apparatus list storage unit  109 , a microcomputer  510 , the CEC communication unit  511 , the TMDS decoding unit  112 , the TMDS input unit  113 , the HDMI input units  114  and  115 , the tuner  120 , and the operation function setting storage unit  121 . 
     The operation mode switching timer  501  includes a timer and an operation mode switching time storage unit. 
     The operation mode switching timer  501  stores the time  1  to switch to the operation mode  1  and the time  2  to switch to the operation mode  2 , via the microcomputer  510 . When the time  1  or the time  2  is reached, the operation mode switching timer  501  notifies the microcomputer  510  that the corresponding set time is reached. 
     The electricity consumption amount storage unit  502  includes a current-day storage unit that temporarily stores an amount of electricity consumption of a current day, and a log recording unit that stores an amount of electricity consumption of a past fixed time period. In the electricity consumption amount storage unit  502 , the current-day storage unit and the log recording unit are connected via CEC, and perform recording for each apparatus that differs in LA and PA. Note that the log recording unit in the electricity consumption amount storage unit  502  is composed of a nonvolatile storage device. 
     The saved electricity consumption amount storage unit  503  includes a current-day storage unit that temporarily stores an amount of saved electricity consumption of the current day, and a log recording unit that stores an amount of saved electricity consumption of the past fixed time period. In the saved electricity consumption amount storage unit  503 , the current-day storage unit and the log recording unit are connected by CEC, and perform recording for each apparatus that differs in LA and PA. Note that the log recording unit in the saved electricity consumption amount storage unit  503  is composed of a nonvolatile storage device. 
     The DVD recorder  60  is an apparatus that records a broadcast signal received via an antenna (not shown), and outputs a recorded video and audio signal via a HDMI cable. As shown in  FIG. 15 , the DVD recorder  60  includes the electricity consumption storage unit  204 , the remote control reception unit  205 , a microcomputer  610 , a CEC communication unit  611 , the decoding unit  212 , the TMDS output unit  213 , the HDMI output unit  214 , the recording timer  217 , the IP communication unit  218 , the recording unit  219 , the tuner  220 , and the operation function setting storage unit  221 . 
     The set-top box  70  is an apparatus that decodes a broadcast signal received via a broadcast signal cable (not shown), and outputs a video and audio signal via a HDMI cable. As shown in  FIG. 16 , the set-top box  70  includes the electricity consumption storage unit  304 , the remote control reception unit  305 , a microcomputer  710 , a CEC communication unit  711 , the decoding unit  312 , the TMDS output unit  313 , the HDMI output unit  314 , the tuner  320 , and the operation function setting storage unit  321 . 
     &lt;Operation&gt; 
     Operations of the TV  50 , the DVD recorder  60 , and the set-top box  70  in the second embodiment are described in detail below. 
     (Operation Mode Switching According to Time) 
     First, the user designates the time  1  to start operation in the power-ON operation mode  1  and the power-OFF operation mode  1  and the time  2  to start operation in the power-ON operation mode  2  and the power-OFF operation mode  2 , through the input unit of the TV  50  beforehand. The TV  50  stores the time  1  and time  2 . 
     When the time  2  designated by the user beforehand is reached, the operation mode switching timer  501  in the TV  50  notifies the microcomputer  510  that the time  2  is reached. 
     The microcomputer  510  receives the notification, and controls the CEC communication unit  511  to transmit an operation mode switching command  2  instructing to switch from the operation mode  1  to the operation mode  2 . 
     The DVD recorder  60  and the set-top box  70  each receive the operation mode switching command and, when the operation mode of the apparatus is the power-ON operation mode  1 , switch the operation mode to the power-ON operation mode  2 . When the operation mode of the apparatus is the power-OFF operation mode  1 , on the other hand, the DVD recorder  60  and the set-top box  70  each switch the operation mode to the power-OFF operation mode  2 . 
     Upon switching the operation mode, the DVD recorder  60  references the operation function setting storage unit  221  in the DVD recorder  60 . For a function that is set to be non-operational in the switched operation mode, the DVD recorder  60  ends a corresponding program or does not energize the function. For a function that is set to be operational in the switched operation mode, the DVD recorder  60  starts a corresponding program or energizes the function. 
     Upon switching the operation mode, the set-top box  70  references the operation function setting storage unit  321  in the set-top box  70 , in the same manner as the DVD recorder  60 . For a function that is set to be non-operational in the switched operation mode, the set-top box  70  ends a corresponding program or does not energize the function. For a function that is set to be operational in the switched operation mode, the set-top box  70  starts a corresponding program or energizes the function. 
     Moreover, when the operation mode of the TV  50  is the power-ON operation mode  1 , the TV  50  switches the operation mode to the power-ON operation mode  2 . When the operation mode of the TV  50  is the power-OFF operation mode  1 , on the other hand, the TV  50  switches the operation mode to the power-OFF operation mode  2 . The TV  50  then starts operation. 
     Subsequently, when the time  1  designated by the user beforehand is reached, the operation mode switching timer  501  in the TV  50  notifies the microcomputer  510  that the time  1  is reached. The microcomputer  510  receives the notification, and controls the CEC communication unit  511  to transmit an operation mode switching command  1  instructing to switch from the operation mode  2  to the operation mode  1 . 
     The DVD recorder  60  and the set-top box  70  each receive the operation mode switching command and, when the operation mode of the apparatus is the power-ON operation mode  2 , switch the operation mode to the power-ON operation mode  1 . When the operation mode of the apparatus is the power-OFF operation mode  2 , on the other hand, the DVD recorder  60  and the set-top box  70  each switch the operation mode to the power-OFF operation mode  1 . 
     Upon switching the operation mode, the DVD recorder  60  references the operation function setting storage unit  221  in the DVD recorder  60 . For a function that is set to be non-operational in the switched operation mode, the DVD recorder  60  ends a corresponding program or does not energize the function. For a function that is set to be operational in the switched operation mode, the DVD recorder  60  starts a corresponding program or energizes the function. 
     Upon switching the operation mode, the set-top box  70  references the operation function setting storage unit  321  in the set-top box  70 , in the same manner as the DVD recorder  60 . For a function that is set to be non-operational in the switched operation mode, the set-top box  70  ends a corresponding program or does not energize the function. For a function that is set to be operational in the switched operation mode, the set-top box  70  starts a corresponding program or energizes the function. 
     Moreover, when the operation mode of the TV  50  is the power-ON operation mode  2 , the TV  50  switches the operation mode to the power-ON operation mode  1 . When the operation mode of the TV  50  is the power-OFF operation mode  2 , on the other hand, the TV  50  switches the operation mode to the power-OFF operation mode  1 . 
     Note that, when the TV  50  is in a power-ON state, the TV  50  does not need to transmit the operation mode switching command. However, in the case where the TV  50  is powered OFF in a period during which the TV  50  is set to operate in the operation mode  2 , that is, a period from the time  2  to the next time  1 , the TV  50  transmits a &lt;Standby&gt; command for powering OFF and also transmits the operation mode switching command  2 . 
     Moreover, when a function of a high priority is operating in the DVD recorder  60  or the set-top box  70  as in the case where, for example, a TV program is being recorded, the DVD recorder  60  or the set-top box  70  buffers the operation mode switching command in the CEC communication unit  611  or  711  and, upon completion of the operation of the function, executes the operation mode switching command. 
     Thus, the TV  50 , the DVD recorder  60 , and the set-top box  70  can switch the operation mode according to the time or time period designated by the user beforehand, through the use of the operation mode switching timer  501 . 
     (Operation Mode Switching in Synchronization with Power ON/OFF) 
     The TV  50 , the DVD recorder  60 , and the set-top box  70  can also switch to the operation mode  1  or the operation mode  2  in synchronization with the user&#39;s operation on the TV  50 , without depending on the operation mode switching timer  501  mentioned above. This is described below. 
     Suppose the user presses an operation mode switching button (not shown) on the remote control  40  of the TV  50  or the cabinet of the TV  50 , when the TV  50  is operating in the operation mode  2 . In this case, the microcomputer  510  in the TV  50  controls the CEC communication unit  511  to transmit an operation mode switching command  3  instructing to switch to the operation mode  1 , to the DVD recorder  60  and the set-top box  70 . 
     The DVD recorder  60  and the set-top box  70  receive the operation mode switching command  3 , switch their operation mode to the power-ON operation mode  1  or the power-OFF operation mode  1 , and start operation. 
     Suppose the user presses the operation mode switching button (not shown) on the remote control  40  of the TV  50  or the cabinet of the TV  50 , when the TV  50  is operating in the operation mode  1 . In this case, the microcomputer  510  in the TV  50  controls the CEC communication unit  511  to transmit an operation mode switching command  4  instructing to switch to the operation mode  2 , to the DVD recorder  60  and the set-top box  70  connected with the TV  50 . 
     Note that, when the TV  50  switches from the operation mode  1  to the operation mode  2 , the TV  50  may be powered OFF and transmit, together with the operation mode switching command  4 , a &lt;Standby&gt; command for powering OFF an apparatus connected via CEC. 
     The DVD recorder  60  and the set-top box  70  receive the operation mode switching command  4 , switch their operation mode to the power-ON operation mode  2  or the power-OFF operation mode  2 , and start operation. 
     In the case where the TV  50  transmits the &lt;Standby&gt; command together with the operation mode switching command  4 , the DVD recorder  60  and the set-top box  70  are powered OFF and switch to the power-OFF operation mode  2 . 
     Thus, the TV  50 , the DVD recorder  60 , and the set-top box  70  can switch to the operation mode  1  or the operation mode  2  without depending on the operation mode switching timer  501 . 
     Note that the operation performed by the user so that the TV  50  transmits the operation mode switching command  3  or the operation mode switching command  4  to switch the operation mode is not limited to the operation mode switching button on the remote control  40  of the TV  50 . For example, a menu item for switching the operation mode may be provided in a menu of the TV  50  so that the operation mode is switched when the user selects the menu item. 
     Moreover, the TV  50  may be powered OFF and transmit the operation mode switching command when a predetermined time period has elapsed without the user&#39;s operation. Furthermore, the TV  50  may learn a tendency as to during which time of day the user operates the TV  50 , and shorten the time period to the power OFF in a time of day during which the user does not tend to operate the TV  50 . This allows for more electrical power saving. 
     (Operation Mode Switching According to User Operation) 
     The TV  50 , the DVD recorder  60 , and the set-top box  70  can also switch the operation mode in synchronization with the user&#39;s operation on the TV  50 , without depending on the operation mode switching timer  501 . Besides, even when the operation mode switching timer  501  has been set, it is possible to switch to the operation mode  3  only in accordance with the user&#39;s operation, without performing operation mode switching by the timer. 
     The following describes switching from the operation mode  1  or the operation mode  2  to the operation mode  3 , and switching from the operation mode  3  to the operation mode  1  or the operation mode  2 . 
     Suppose the user presses the operation mode switching button (not shown) on the remote control  40  of the TV  50  or the cabinet of the TV  50 , when the TV  50  is operating in the operation mode  1  or the operation mode  2 . In this case, the microcomputer  510  in the TV  50  controls the CEC communication unit  511  to transmit an operation mode switching command  5  instructing to switch to the operation mode  3 , to the DVD recorder  60  and the set-top box  70  connected with the TV  50 . 
     Note that, when the TV  50  switches from the operation mode  1  or the operation mode  2  to the operation mode  3 , the TV  50  may be powered OFF and transmit, together with the operation mode switching command  5 , a &lt;Standby&gt; command for powering OFF an apparatus connected via CEC. 
     The DVD recorder  60  and the set-top box  70  receive the operation mode switching command  5 , and switch their operation mode to the power-OFF operation mode  3 . 
     In the case where the TV  50  transmits the &lt;Standby&gt; command together with the operation mode switching command  5 , the DVD recorder  60  and the set-top box  70  are powered OFF and switch to the operation mode  3 . 
     Suppose the user presses the operation mode switching button (not shown) on the remote control  40  of the TV  50  or the cabinet of the TV  50 , when the TV  50  is operating in the operation mode  3 . In this case, the microcomputer  510  in the TV  50  controls the CEC communication unit  511  to transmit an operation mode switching command  6  instructing to clear the operation mode  3 , to the DVD recorder  60  and the set-top box  70  connected with the TV  50 . 
     Here, the TV  50  adds a parameter to the operation mode switching command  6  so as to switch to the operation mode  1  or the operation mode  2  after clearing the operation mode  3 , and transmits the operation mode switching command  6 . For example, in the case of transmitting the operation mode switching command  6  in a period from the time  1  to the time  2 , the TV  50  adds the parameter so as to switch to the operation mode  1 . In the case of transmitting the operation mode switching command  6  in a period from the time  2  to the next time  1 , the TV  50  adds the parameter so as to switch to the operation mode  2 . 
     The DVD recorder  60  and the set-top box  70  receive the operation mode switching command  6 , switch their operation mode to the power-ON operation mode  1  or  2  or the power-OFF operation mode  1  or  2 , and start operation. 
     Thus, the TV  50 , the DVD recorder  60 , and the set-top box  70  can switch from the operation mode  1  or the operation mode  2  to the operation mode  3  on the basis of the received control command, without depending on the operation mode switching timer  501 . 
     Note that the operation performed by the user so that the TV  50  transmits the operation mode switching command  5  or the operation mode switching command  6  to switch the operation mode is not limited to the press of the operation mode switching button on the remote control  40  of the TV  50 . For example, the operation mode may be switched when the user presses the power button on the remote control  40 . Alternatively, a menu item for switching the operation mode may be provided in a menu of the TV  50  so that the operation mode is switched when the user selects the menu item. Moreover, the switching to the operation mode  3  may be performed when there is no user operation within a predetermined time period, such as 24 hours, after the user powers OFF the TV  50 . Furthermore, the TV  50  may learn a tendency as to during which time of day the user operates the TV  50 , and shorten the time period to switch to the operation mode  3  in a time of day during which the user does not tend to operate the TV  50 . 
       FIG. 17  shows an example of an OSD menu for setting a function that is operational in the operation mode  3  and switching to the operation mode  3  in the TV  50  according to the present invention. 
     For instance, the TV  50  displays a menu such as an OSD menu  3100  shown in  FIG. 17 . When the user selects a desired menu item, the CEC communication unit  511  in the TV  50  transmits an operation function setting update command that includes information for setting a function combination corresponding to the menu item to be operational in the operation mode  3 , to the DVD recorder  60  and the set-top box  70 . The CEC communication unit  511  also transmits the operation mode switching command  5  instructing to switch to the operation mode  3 , to the DVD recorder  60  and the set-top box  70 . Upon receiving the operation function setting update command, the DVD recorder  60  and the set-top box  70  update the operation function setting storage units  221  and  321  so that the function combination shown by the operation function setting update command is set as a function operational in the operation mode  3 . 
     The DVD recorder  60  and the set-top box  70  also receive the operation mode switching command  5 , switch to the operation mode  3 , and start operation in the operation mode  3 . 
     Thus, the TV  50 , the DVD recorder  60 , and the set-top box  70  can switch the operation mode in accordance with the user&#39;s operation. 
     (Operations of the DVD Recorder  60  and the Set-Top Box  70  When the TV  50  is in a Power-ON State) 
     When video and audio data outputted from the DVD recorder  60  cannot be reproduced in the TV  50  as in the case where the user is viewing video and audio from the set-top box  70  in the TV  50  in the operation mode  1  or the operation mode  2 , the DVD recorder  60  is powered OFF. 
     Likewise, when video and audio data outputted from the set-top box  70  cannot be reproduced in the TV  50  as in the case where the input of the TV  50  is the DVD recorder  60 , the set-top box  70  is powered OFF. 
       FIG. 18  shows an example of a flow of CEC command transmission and reception when the DVD recorder  60  and the set-top box  70  operate according to the user&#39;s operation in the second embodiment of the present invention. The following describes a process whereby the DVD recorder  60  and the set-top box  70  are powered OFF according to the user&#39;s viewing operation of the TV  50 , with reference to  FIG. 18 . 
     First, the user powers ON the TV  50  by performing an input operation through the input unit of the TV  50  such as the remote control  40  (Step S 201 ). 
     After the TV  50  is powered ON, in the case of reproducing video and audio from the tuner  120  included in the TV  50 , the TV  50  broadcasts an &lt;Active Source&gt; command to the DVD recorder  60  and the set-top box  70 . 
     The TV  50  also transmits an activation notification command from the CEC communication unit  511  to the DVD recorder  60  and the set-top box  70 . 
     The microcomputers  610  and  710  in the DVD recorder  60  and the set-top box  70  receive the activation notification command from the CEC communication units  611  and  711 , and reference the operation function setting storage units  221  and  321 , respectively. In each of the DVD recorder  60  and the set-top box  70 , when the apparatus is in the operation mode  1 , the microcomputer activates a function that is operational in a power-ON state of the TV  50  in the power-OFF operation mode  1 . When the apparatus is in the operation mode  2 , on the other hand, the microcomputer activates a function that is operational in a power-ON state of the TV  50  in the power-OFF operation mode  2 . 
     Next, to start viewing the set-top box  70 , the user performs selection by selecting a menu displayed on the TV  50  or pressing a button on the remote control  40  of the TV  50  (Step S 204 ). 
     The TV  50  responsively transmits a power-ON command to the set-top box  70  (Step S 205 ). 
     The set-top box  70  receives the power-ON command, transitions to a power-ON state, and starts outputting video and audio. When starting the video and audio output, the set-top box  70  transmits an &lt;Active Source&gt; command to the TV  50  and the DVD recorder  60 . 
     Upon receiving the &lt;Active Source&gt; command, the TV  50  stores a LA and a PA of the transmitter of the command, in the active source apparatus storage unit  108  in the TV  50 . 
     Next, to start viewing the DVD recorder  60 , the user performs selection by selecting a menu displayed on the TV  50  or pressing a button on the remote control  40  of the TV  50  (Step S 207 ). 
     The TV  50  responsively transmits a power-ON command to the DVD recorder  60  (Step S 208 ). 
     The DVD recorder  60  receives the power-ON command, transitions to a power-ON state, and starts outputting video and audio. When starting the video and audio output, the DVD recorder  60  transmits an &lt;Active Source&gt; command to the TV  50  and the set-top box  70 . 
     Upon receiving the &lt;Active Source&gt; command, the TV  50  references the active source apparatus storage unit  108  in the TV  50 . When a PA of the transmitter of the received command does not match the PA in the active source apparatus storage unit  108 , the TV  50  determines that the active source is changed. The TV  50  transmits a power-OFF command to the LA in the active source apparatus storage unit  108 , that is, the set-top box  70  in this embodiment (Step S 209 ). 
     The TV  50  also stores a LA and the PA of the transmitter of the &lt;Active Source&gt; command, in the active source apparatus storage unit  108 . 
     The set-top box  70  receives the power-OFF command, and transitions to a power-OFF state. Here, in Step S 209 , the microcomputer  710  in the set-top box  70  references the operation function setting storage unit  321 . 
     When the set-top box  70  is in the operation mode  1 , the microcomputer  710  ends an unnecessary function so as to operate only a function that is operational in a power-ON state of the TV  50  in the power-OFF operation mode  1 . When the set-top box  70  is in the operation mode  2 , the microcomputer  710  ends an unnecessary function so as to operate only a function that is operational in a power-ON state of the TV  50  in the power-OFF operation mode  2 . 
     Next, the user operates the remote control  40  of the set-top box  70  to start video and audio output. The set-top box  70  transmits an &lt;Active Source&gt; command from the CEC communication unit  711  to the TV  50  and the DVD recorder  60  (Step S 213 ). 
     Upon receiving the &lt;Active Source&gt; command from the set-top box  70 , the TV  50  references the active source apparatus storage unit  108 . When the active source is changed, the TV  50  transmits a power-OFF command to the LA in the active source apparatus storage unit  108 , that is, the DVD recorder  60  (Step S 214 ). 
     The DVD recorder  60  receives the power-OFF command, and transitions to a power-OFF state. 
     Here, the microcomputer  610  in the DVD recorder  60  references the operation function setting storage unit  221 . When the DVD recorder  60  is in the operation mode  1 , the microcomputer  610  ends an unnecessary function so as to operate only a function that is operational in a power-ON state of the TV  50  in the power-OFF operation mode  1 . When the DVD recorder  60  is in the operation mode  2 , the microcomputer  610  ends an unnecessary function so as to operate only a function that is operational in a power-ON state of the TV  50  in the power-OFF operation mode  2 . 
     Note that, when transmitting the power-OFF command, the TV  50  may notify the user that the connected apparatus is powered OFF. For example, when the user switches to the set-top box  70  while viewing the DVD recorder  60 , the TV  50  transmits the power-OFF command to the DVD recorder  60 , and also notifies the user that the DVD recorder  60  is powered OFF, through a display such as an OSD display  3201  shown in  FIG. 19  in the video output device. 
     When the user presses an input selection button of the TV  50 , the TV  50  transmits a &lt;Set Stream Path&gt; command having, as a parameter, a PA of an apparatus connected to a designated input. 
     In this case, the DVD recorder  60  or the set-top box  70  is powered ON and transmits an &lt;Active Source&gt; command, when the PA shown by the parameter in the &lt;Set Stream Path&gt; command is the same as the PA of the apparatus. The DVD recorder  60  or the set-top box  70  then starts outputting video and audio data. 
     Note that, when a function of a high priority is operating as in the case where, for example, a TV program is being recorded, the DVD recorder  60  or the set-top box  70  buffers the power-OFF command in the CEC communication unit  611  or  711  and, upon completion of the operation of the function, executes the power-OFF command. 
     In the above way, the DVD recorder  60  and the set-top box  70  can each be powered OFF according to the user&#39;s viewing operation on the TV  50 . By ending an unnecessary function when the user is not viewing the apparatus, it is possible to reduce electricity consumption. 
     (Electricity Consumption Amount Recording) 
     The TV  50 , the DVD recorder  60 , and the set-top box  70  each record an amount of electricity consumption, i.e., an amount of electrical power consumed in the apparatus, and an amount of saved electricity consumption achieved as a result of a change in operation state caused by the operation mode switching timer. 
     In addition, in each of the TV  50 , the DVD recorder  60 , and the set-top box  70 , a correspondence table of each operation state and electricity consumption of the apparatus in the operation state is stored in the electricity consumption storage unit ( 104 ,  204 , and  304 ) beforehand. Note that, when there is no significant difference in electricity consumption between operational function combinations, such combinations may be shown together as one state. 
     The following describes a process whereby the TV  50  obtains an amount of electricity consumption and an amount of saved electricity consumption in the DVD recorder  60 . Note that the correspondence of each operation state and electricity consumption in the DVD recorder  60  is the same as that in the DVD recorder  20  in the first embodiment. 
     First, the TV  50  transmits an operation state electricity consumption request command to the DVD recorder  60 , at regular time intervals such as 1-hour intervals. 
     Upon receiving the operation state electricity consumption request command, the DVD recorder  60  references the electricity consumption storage unit  204  to obtain electricity consumption in a current operation state. The DVD recorder  60  transmits an operation state electricity consumption notification command having, as a parameter, information showing the current operation state and the current electricity consumption, to the TV  50 . 
     The TV  50  receives the operation state electricity consumption notification command, and calculates a product of the electricity consumption of the DVD recorder  60  shown by the parameter in the operation state electricity consumption notification command and the transmission time interval of the operation state electricity consumption request command. The TV  50  adds the product to a value stored in the electricity consumption amount storage unit  502 . In this way, the amount of electricity consumption of the DVD recorder  60  is stored in the electricity consumption amount storage unit  502 . 
     Moreover, the TV  50  transmits an operation state saved electricity request command to the DVD recorder  60 , at regular time intervals such as 1-hour intervals. 
     The DVD recorder  60  receives the operation state saved electricity request command. When the current operation state is caused by the above-mentioned operation mode switching, the DVD recorder  60  transmits an operation state saved electricity notification command having, as a parameter, a difference between electricity consumption in a normal operation state and the electricity consumption in the current operation state, to the TV  50 . 
     The TV  50  receives the operation state saved electricity notification command, and calculates a product of the electricity consumption difference shown by the parameter in the command and the transmission time interval of the operation state saved electricity request command. The TV  50  adds the product to a value stored in the saved electricity consumption amount storage unit  503 . In this way, the amount of saved electricity consumption of the DVD recorder  60  is stored in the saved electricity consumption amount storage unit  503 . 
     In addition, having received the operation state electricity consumption notification command and the operation state saved electricity notification command, the TV  50  displays the current operation state of the apparatus transmitting the commands on the screen of the TV  50 , as shown by an OSD display  3301  in  FIG. 20 . 
     Furthermore, the electricity consumption amount storage unit  502  in the TV  50  stores a pair of a value corresponding to the current day and a recording date and time in the log recording unit in the electricity consumption amount storage unit  502 , at regular time intervals such as 24-hour intervals. Having stored the pair of the amount of electricity consumption for the regular time interval and the recording time in the recording unit in this way, the electricity consumption amount storage unit  502  resets the value in the current-day storage unit in the electricity consumption amount storage unit  502  to 0. 
     Note that the time intervals of recording a log of the amount of electricity consumption and the amount of saved electricity consumption are not limited to 24-hour intervals, so long as they are regular time intervals. Here, the log recording unit records, for example, a log corresponding to 30 days, and deletes the log in order of occurrence when 30 days are exceeded. 
     Moreover, having received the operation state electricity consumption notification command and the operation state saved electricity notification command, the TV  50  may display not only the operation state of the apparatus but also the current electricity consumption. 
     Here, electricity consumption or saved electricity may be displayed, using a numeric value of electricity, a ratio to maximum electricity consumption in the apparatus, or an icon that changes in proportion to the numeric value of electricity or the ratio of electricity. 
     In this way, the TV  50  can obtain the amount of electricity consumption and the amount of saved electricity consumption of the DVD recorder  60 . 
     The TV  50  can equally obtain the amount of electricity consumption and the amount of saved electricity consumption of the set-top box  70 , as a result of the transmission of the operation state electricity consumption request command and the operation state saved electricity request command. 
     (Electricity Consumption Amount Display by the TV  50 ) 
     The following describes the case where the user operates the remote control  40  of the TV  50  or a menu of the TV  50  to display an amount of electricity consumption and an amount of saved electricity consumption. 
     First, the TV  50  references the electricity consumption amount storage unit  502  and the saved electricity consumption amount storage unit  503  in the TV  50 , and obtains electricity consumption amount information and saved electricity consumption amount information. The TV  50  calculates a total amount of electricity consumption of the apparatuses, and displays the amount of electricity consumption on a daily basis. For example, as shown by the OSD display  2002  in  FIG. 12 , an amount of electricity consumption from 30 days ago up to 1 day ago is displayed where a horizontal axis represents a time and a vertical axis represents an amount of electricity consumption. In the same manner, the TV  50  calculates a total amount of saved electricity consumption on a daily basis and displays it on the screen. 
     Here, values stored in the electricity consumption amount storage unit  502  and the saved electricity consumption amount storage unit  503  in the TV  50  may be added respectively to the displayed amount of electricity consumption and amount of saved electricity consumption. 
     Moreover, the amount of electricity consumption and the amount of saved electricity consumption may be OSD-displayed when the user powers ON the TV  50  and the TV  50  starts video output. 
     Thus, the amount of electricity consumption and the amount of saved electricity consumption of the TV  50 , the DVD recorder  60 , and the set-top box  70  can be displayed to the user. 
     Note that the power control of each component is not limited to the microcomputer or the like shown in the above embodiments, and may instead be performed by another power control unit that performs only power control. 
     The first and second embodiments describe an example where the TV, as a master apparatus in the AV system, transmits a control command to the DVD recorder and the set-top box to thereby switch the operation mode of the DVD recorder and the set-top box. However, the present invention is not limited to such, and the DVD recorder or the set-top box may serve as the master in the AV system. 
     Moreover, the first and second embodiments describe the case where the TV, the DVD recorder, and the set-top box are connected in the AV system, but this is not a limit for the present invention. For example, as shown in  FIG. 21 , the TV  50 , an AV amplifier  65 , and the set-top box  70  may be connected in the AV system. In this case, for example, the AV amplifier  65  has a plurality of operation modes as shown in  FIG. 22 , where the AV amplifier  65  in a power-OFF state has at least the power-OFF operation mode  1  and the power-OFF operation mode  2 . The structures and operations in this case are the same as those in the first and second embodiments, and so their description is omitted. 
     As described above, in the AV system where a plurality of apparatuses that each have a plurality of operation states of different electricity consumption are connected via a communication network such as HDMI, the plurality of operation states can be controlled so as to improve electricity consumption efficiency in the AV system. In detail, suppose one apparatus has the power-OFF operation mode  1  in which the apparatus is in a power-OFF state but a part of the apparatus is supplied with power, and the power-OFF operation mode  2  in which fewer functions are operational than in the power-OFF operation mode  1  and therefore electricity consumption is lower than the power-OFF operation mode  1 . For example, the apparatus which is in the power-OFF operation mode  1  switches its operation state to the power-OFF operation mode  2  of lower electricity consumption, on the basis of a control command or the like received from a master apparatus. Such control contributes to efficient electricity consumption of the apparatus. 
     Thus, according to the present invention, an operation state of a connected apparatus is switched by a control command or the like of another apparatus, with it being possible to improve electricity consumption efficiency. Hence, an electrical power saving system that achieves efficient electricity consumption of apparatuses connected via a communication network can be realized. 
     Note that the TV in the AV system described above is one embodiment of a video display apparatus capable of displaying video, and the video display apparatus is one particular embodiment of the first apparatus according to the present invention. Likewise, each of the DVD recorder and the set-top box is one embodiment of a video recording apparatus capable of recording and reproducing video, and the video recording apparatus is one particular embodiment of the second apparatus according to the present invention. 
     Although the electrical power saving system according to the present invention has been described by way of the above embodiments, the present invention is not limited to the above embodiments. Applying various changes conceivable by a person skilled in the art to the embodiments and combining components in the different embodiments are also included in the scope of the present invention without departing from the principles of the present invention. 
     The present invention is applicable to an electrical power saving system. In particular, the present invention is applicable to an electrical power saving system, such as an AV system, in which an operation mode is switched by performing transmission and reception of a control command between apparatuses connected via a communication network.