Patent Publication Number: US-2017359776-A1

Title: Wireless communication device which reduce power consumption

Description:
The present U.S. patent application claims a priority under the Paris Convention of Japanese patent application No. 2016-117979 filed on Jun. 14, 2016, the entirety of which is incorporated herein by references. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a wireless communication device and a control program for a wireless communication device. More specifically, this invention relates to a wireless communication device and a control program for a wireless communication device which can reduce the power consumption. 
     Description of the Related Art 
     There are an MFP (Multi Function Peripheral) having a scanner function, a facsimile function, a copying function, a function of a printer, a data transmitting function and a server function, a facsimile device, a copying machine, a printer, and so on, as electrophotography image forming apparatuses. 
     Recently, as wireless communication techniques, techniques of the Wifi direct, the beam forming, and so on are spreading. The Wifi direct is one of standards in which direct wireless communication between equipments is performed without going through a relay device such as an access point, a rooter, or the like. The beam forming is a technique to improve communication efficiency, by emitting radio waves of which the phases are optimized with locally strong intensity to a direction in which a receiving side equipment exists from a transmitting side equipment. 
     Conventional techniques which relate to wireless communication are disclosed in the below Documents 1 to 3, for example. 
     The below Document 1 discloses a technique to acquire lowest transmitting electric power of a communication terminal which establishes a connection with a wireless network access point, and adjust and determine transmitting electric power of the communication terminal according to the lowest transmitting electric power. The lowest transmitting electric power is minimum transmitting electric power which can ensure connection and communication between the communication terminal and the wireless network access point. 
     The below Document 2 discloses a portable terminal device which determines whether the location of the portable terminal device is within an available area, based on the location information of the portable terminal device. As for executing a function for which usage restriction was configured, when it is determined that the location is within the available area, this portable terminal device cancels the usage restriction regardless of the authentication. 
     The below Document 3 discloses a wireless authentication system comprising a carrier generating unit for generating a carrier wave, a modulation signal generating unit for modulating the carrier wave generated by the carrier generating unit, a duty ratio variable unit for varying the duty of the modulation signal output from the modulation signal generating unit, and an amplifier unit for amplifying the modulation signal having the duty configurated by the duty ratio variable unit and driving an LF antenna by the amplificated electrical voltage pulse. 
     PRIOR ART DOCUMENT(S) 
     Document(s) Related to Patent(s) 
     [Document 1] Japanese Translation of PCT International Application Publication No. 2013-535906 
     [Document 2] Japan Patent Publication No. 2012-085121 
     [Document 3] Japan Patent Publication No. 2008-219509 
     Conventionally, when an MFP not having the beam forming function performs wireless communication with a portable terminal device by the Wifi direct, the MFP emits radio waves for the wireless communication with constant intensity. Therefore, waste of power consumption occurs, when a portable terminal device which is going to be more likely to perform wireless communication with the MFP does not exist near the MFP, or the intensity of radio waves that a portable terminal device as a target of the wireless communication receives from the MFP is adequately high. 
     Conventionally, when an MFP having the beam forming function performs wireless communication with a portable terminal device by the Wifi direct, the MFP unconditionally performs the beam forming to all portable terminal devices which exist near the MFP. Therefore, waste of power consumption occurs, when the possibility of wireless communication of the portable terminal devices which exist near the MFP with the MFP is low, or the intensity of radio waves that a portable terminal device as a target of wireless communication receives from the MFP is already high adequately. 
     SUMMARY OF THE INVENTION 
     This invention is to solve the above problems. The object is to provide a wireless communication device which can reduce the power consumption and a control program for the wireless communication device. 
     To achieve at least one of the abovementioned objects, according to an aspect, a wireless communication device capable of executing direct wireless communication with each of a plurality of communication apparatuses, without intermediary equipment, reflecting one aspect of the present invention comprise: an emitting device to emit radio waves for the direct wireless communication, a determination unit to determine whether a new communication apparatus which is one of the plurality of the communication apparatuses satisfies a specified condition or not, when the direct wireless communication starts with the new communication apparatus, a target determination unit to regard the new communication apparatus as a communication maintenance target, when the determination unit determined that the new communication apparatus satisfies the specified condition, and an adjustment unit to weaken intensity of radio waves which the emitting device emits, so that the intensity of radio waves which the emitting device emits and a communication apparatus which is the communication maintenance target receives is within a predetermined range in which the direct wireless communication can be maintained. 
     According to another aspect for a non-transitory computer-readable recording medium storing a controlling program for a wireless communication device capable of executing direct wireless communication with each of a plurality of communication apparatuses, without intermediary equipment, reflecting one aspect of the present invention, the wireless communication device comprises an emitting device to emit radio waves for the direct wireless communication, and the controlling program causes a computer to execute the steps to: determine whether a new communication apparatus which is one of the plurality of the communication apparatuses satisfies a specified condition or not, when the direct wireless communication starts with the new communication apparatus, regard the new communication apparatus as a communication maintenance target, when the determination step determined that the new communication apparatus satisfies the specified condition, and weaken the intensity of radio waves the emitting device emits, so that an intensity of radio waves the emitting device emits and a communication apparatus which is the communication maintenance target receives is within a predetermined range in which the direct wireless communication can be maintained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein: 
         FIG. 1  roughly shows a structure of an image forming system according to the first embodiment of this invention. 
         FIG. 2  shows a block diagram indicating a structure of MFP  100 , according to the first embodiment of this invention. 
         FIG. 3  shows a block diagram indicating a structure of a portable terminal device  200 , according to the first embodiment of this invention. 
         FIG. 4  shows a block diagram indicating a structure of a server  300 , according to the first embodiment of this invention. 
         FIG. 5  shows an example of a user information table  121  stored in storage device  104  of MFP  100 , according to the first embodiment of this invention. 
         FIG. 6  shows the first figure indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
         FIG. 7  shows the second figure indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
         FIG. 8  shows an example of the adjustment method for the intensity of radio waves emitted from wireless communication unit  122 , according to the first embodiment of this invention. 
         FIG. 9  shows the third figure indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
         FIG. 10  shows the fourth figure indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
         FIG. 11  shows the fifth figure indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
         FIG. 12  schematically shows a screen for receiving configurations of a connection area displayed on a display unit DP in an operation panel  108 , according to the first embodiment of this invention. 
         FIG. 13  shows the first part of a flowchart indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
         FIG. 14  shows the second part of a flowchart indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
         FIG. 15  shows a subroutine of the communication maintenance target determining process (S 115 ) in  FIG. 13 . 
         FIG. 16  shows an example of entering/leaving room table  321  stored in storage device  304  of the server  300 , according to the second embodiment of this invention. 
         FIG. 17  shows the first figure indicating the behavior of MFP  100 , according to the second embodiment of this invention. 
         FIG. 18  shows the second figure indicating the behavior of MFP  100 , according to the second embodiment of this invention. 
         FIG. 19  shows the third figure indicating the behavior of MFP  100 , according to the second embodiment of this invention. 
         FIG. 20  shows the first part of a flowchart indicating the behavior of MFP  100 , according to the second embodiment of this invention. 
         FIG. 21  shows the second part of a flowchart indicating the behavior of MFP  100 , according to the second embodiment of this invention. 
         FIG. 22  shows the first figure indicating the behavior of MFP  100 , according to the third embodiment of this invention. 
         FIG. 23  shows an example of the adjustment method of the intensity of radio waves emitted from wireless communication unit  122 , according to the third embodiment of this invention. 
         FIG. 24  shows the second figure indicating the behavior of MFP  100 , according to the third embodiment of this invention. 
         FIG. 25  shows the third figure indicating the behavior of MFP  100 , according to the third embodiment of this invention. 
         FIG. 26  shows the first part of a flowchart indicating the behavior of MFP  100 , according to the third embodiment of this invention. 
         FIG. 27  shows the second part of a flowchart indicating the behavior of MFP  100 , according to the third embodiment of this invention. 
         FIG. 28  shows the first figure indicating the behavior of MFP  100 , according to the fourth embodiment of this invention. 
         FIG. 29  shows the second figure indicating the behavior of MFP  100 , according to the fourth embodiment of this invention. 
         FIG. 30  shows the third figure indicating the behavior of MFP  100 , according to the fourth embodiment of this invention. 
         FIG. 31  shows the first half part of a flowchart indicating the behavior of MFP  100 , according to the fourth embodiment of this invention. 
         FIG. 32  shows the latter half part of a flowchart indicating the behavior of MFP  100 , according to the fourth embodiment of this invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples. 
     In the following embodiments, a wireless communication device as an MFP will be explained. A wireless communication device may be an image forming apparatus such as a facsimile device, a copying machine, or a printer, other than an MFP. A wireless communication device may be any device as long as the wireless communication device can execute the direct wireless communication with a plurality of portable terminal devices without intermediary equipment. A wireless communication device may be a PC (Personal Computer), a mobile terminal, a home electrical appliance, or the like. 
     The First Embodiment 
       FIG. 1  roughly shows a structure of an image forming system according to the first embodiment of this invention. 
     Referring to  FIG. 1 , an image forming system according to the embodiment is equipped with a plurality of MFPs  100  (examples of a plurality of wireless communication devices), a plurality of portable terminal devices  200  (examples of a plurality of communication apparatuses), a server  300 , and a plurality of PCs  400 . The plurality of MFPs  100 , the plurality of portable terminal devices  200 , the server  300 , and the plurality of PCs  400  are connected with each other via network NT, to perform bilaterally communication. 
     Network NT uses a private line such as a wired or wireless LAN (Local Area Network), for example. Network NT connects various equipment by using the protocol of TCP/IP (Transmission Control Protocol/Internet Protocol). The equipment connected to network NT can transmit and receive various data with each other. An access point AP is provided in network NT. When two devices connected to the network perform wireless communication, these devices can execute wireless communication via the access point AP. The image forming system may comprise equipments connected to the network NT, other than the above mentioned equipments. 
     In addition to the above mentioned communication via network NT, each of the plurality of MFPs  100  and each of the plurality of portable terminal devices  200  can execute the direct wireless communication bilaterally, without an intermediary equipment such as the access point AP, by using the Wifi direct standard or the like. 
       FIG. 2  shows a block diagram indicating a structure of MFP  100 , according to the first embodiment of this invention. 
     Referring to  FIG. 2 , MFP  100  includes CPU (Central Processing Unit)  101 , ROM (Read Only Memory)  102 , RAM (Random Access Memory)  103 , storage device  104 , network I/F  105 , print processing unit  106 , image processing unit  107 , operation panel  108 , scanner unit  109 , user authentication unit  110 , and so on. ROM  102 , RAM  103 , storage device  104 , network I/F  105 , print processing unit  106 , image processing unit  107 , operation panel  108 , scanner unit  109 , and user authentication unit  110  are connected to CPU  101  via the bus. 
     CPU  101  controls the entire MFP  100  for various jobs such as a scan job, a copy job, a mail transmitting job, and a print job, for example. CPU  101  executes control programs stored in ROM  102 . 
     ROM  102  is a flash ROM, for example. ROM  102  stores various programs and various fixed data to perform the behavior of MFP  100 . ROM  102  may not be rewritable. 
     RAM  103  is a main memory for CPU  101 . RAM  103  is used to temporarily store data required when CPU  101  executes a control program and image data. RAM  103  temporarily store the configuration accepted from a user for a job to be executed by MFP  100 . 
     Storage device  104  is equipped with a HDD (Hard Disk Drive), for example, to store user information table  121  ( FIG. 5 ), the location information where the MFP is installed, various data for the behavior of MFP  100 , and so on. 
     Network I/F  105  performs communication with equipments connected to the network NT by the communications protocol such as TCP/IP, in accordance with instructions from CPU  101 . Network I/F  105  includes wireless communication unit  122  (an example of an emitting device). Wireless communication unit  122  executes the direct wireless communication with portable terminal devices  200 . Wireless communication unit  122  emits radio waves for the direct wireless communication, and receives radio waves transmitted from portable terminal devices  200  for the direct wireless communication. 
     Unless otherwise mentioned, it is supposed that wireless communication unit  122  has the beam forming function to locally emit radio waves with strong intensity toward the direction in which a specified portable terminal device  200  exists. 
     Print processing unit  106  executes print processes to form images on sheets or the like, based on image data processed by images processing unit  107 , in accordance with an instruction of performing a printing job received from any one of the plurality of portable terminal devices. 
     Images processing unit  107  executes the RIP (Raster image processing) process with respect to printing data, in accordance with an instruction of performing a printing job received from any one of the plurality of portable terminal devices, the converting process to convert the data format when transmitting data to the outside, and so on. 
     Operation panel  108  includes a display unit which consists of a touch panel display and so on, an inputting portion which consists of hardware keys, software keys displayed on the touch panel display, and so on. Operation panel  108  receives the configuration which relates to a job to be executed by MFP  100 , from a user. Operation panel  108  displays various configuration items which relate to MFP  100 , messages, and so on, to a user. Operation panel  108  may have the NFC (Near Field Radio Communication) function. 
     Scanner unit  109  reads document images. 
     User authentication unit  110  authenticates the user based on a user ID stored in an ID (Identification) card possessed by each of the users, a user ID and a password input from operation panel  108  or portable terminal device  200 , the IP address of the portable terminal device  200 , or the like, to allow the user authenticated to use MFP  100 . 
       FIG. 3  shows a block diagram indicating a structure of a portable terminal device  200 , according to the first embodiment of this invention. 
     Referring to  FIG. 3 , a portable terminal device  200  includes CPU  201 , ROM  202 , RAM  203 , storage device  204 , wireless communication unit  205 , operation unit  206 , display unit  207 , and GPS (Global Positioning System) information acquire unit  208 . Each of ROM  202 , RAM  203 , storage device  204 , wireless communication unit  205 , operation unit  206 , display unit  207  and GPS information acquire unit  208  is connected to CPU  201  via the bus. 
     CPU  201  controls the entire portable terminal device  200 . CPU  201  executes control programs stored in ROM  202 . 
     ROM  202  is a flash ROM, for example. ROM  202  stores various programs and so on, to perform the behavior of portable terminal device  200 . 
     RAM  203  is a main memory for CPU  201 . RAM  203  is used to temporarily store data required when CPU  201  executes the control programs. 
     Storage device  204  comprises a HDD, for example, to store various data. 
     Wireless communication unit  205  executes the direct wireless communication with MFP  100 . Wireless communication unit  205  emits radio waves for the direct wireless communication, and receives radio waves transmitted from MFP  100  for the direct wireless communication. 
     Operation unit  206  receives various instructions which relate to portable terminal device  200 , from a user. 
     Display unit  207  displays various information which relates to portable terminal device  200 . 
     GPS information acquire unit  208  acquires information (the location information) indicating the location of portable terminal device  200  by using the GPS system. 
       FIG. 4  shows a block diagram indicating a structure of a server  300 , according to the first embodiment of this invention. 
     Referring to  FIG. 4 , server  300  executes the administration of entering/leaving room, for a room in which MFP  100  is installed. Server  300  includes CPU  301 , ROM  302 , RAM  303 , storage device  304 , network I/F  305 , operation unit  306 , display unit  307 , and so on. Each of ROM  302 , RAM  303 , storage device  304 , network I/F  305 , operation unit  306  and display unit  307  is connected to CPU  301  via the bus. 
     CPU  301  controls the entire server  300 . CPU  301  executes control programs stored in ROM  302 . 
     ROM  302  is a flash ROM, for example. ROM  302  stores various programs to perform the behavior of server  300 , and various fixed data. ROM  302  may not be rewritable. 
     RAM  303  is a main memory for CPU  301 . RAM  303  is used to temporarily store data required when CPU  301  executes control programs, image data, and so on. RAM  303  may have a cache memory area for CPU  301 . 
     Storage device  304  comprises a HDD, for example, to store various data for the behavior of server  300  such as entering/leaving room table  321  and so on. 
     Network I/F  305  performs communication with MFP  100  via network NT, by communications protocol such as the TCP/IP, in accordance with instructions from CPU  301 . 
     Operation unit  306  receives various instructions which relate to server  300 , from a user. 
     Display unit  307  displays various information which relates to server  300 . 
       FIG. 5  shows an example of a user information table  121  stored in storage device  104  of MFP  100 , according to the first embodiment of this invention. 
     Referring to  FIG. 5 , user information table  121  is a table on which information related to users of MFP  100  is recorded. The user information table includes items in which users are recorded, items in which portable terminal devices possessed by the users are recorded, items in which connection areas (examples of predetermined communication ranges) of portable terminal devices possessed by the users are recorded, items in which storing areas (boxes) associated with the users in storage device  104  are recorded, items in which facsimile transmitting addresses of the users are recorded, and items in which the usage histories for jobs on MFP  100  executed by the users via the portable terminal devices are recorded. As the usage histories, up to four histories are recorded from the new one. 
     According to user information table  121 , for example, the “user A” has the portable terminal device named “portable terminal device A” and the storing area named “BOX_A” in storage device  104 , and the facsimile transmitting address of “FAX_address A” is recorded in storage device  104 . The “user A” has 4 histories, wherein the newest usage history is for a print job executed on “Mar. 14, 2016”. 
     The user A, the user B, and the user C have storing areas in storage device  104 , and the facsimile transmitting addresses are recorded in storage device  104 . On the other hand, the user D, the user E, and the user F do not have storing areas in storage device  104 , the facsimile transmitting addresses are not recorded in storage device  104 . Unless otherwise noted, for all the portable terminal devices of the users, it is supposed that the same connection area of “30 m to the right, 20 m to the left, 30 m to the front side, 10 m to the back side” using the location at which MFP  100  is installed as a reference is configured. 
     User information table  121  may further include items in which the mail addresses of users are recorded. The information such as portable terminal devices, connection areas, boxes, facsimile transmitting addresses, and mail addresses are beforehand registered by users, an administrator of MFP  100 , or the like. The usage histories of MFP  100  are updated by CPU  101  at the timing of the job execution. 
     User information table  121  may be recorded in storage device  304  of server  300 . 
     Next, the behavior of MFP  100  according to the embodiment will be explained by using  FIGS. 6 to 11 . 
     When MFP  100  begins to perform the direct wireless communication with a new portable terminal device which is one of the plurality of portable terminal devices, MFP  100  determines whether the new portable terminal device satisfies a specified condition or not. When the new portable terminal device satisfies the specified condition, MFP  100  regards the new portable terminal device as a communication maintenance target. MFP  100  weakens the intensity of radio waves which wireless communication unit  122  emits, so that the intensity of radio waves received by the portable terminal device as the communication maintenance target, which is radio waves emitted from wireless communication unit  122  is within a predetermined range in which the direct wireless communication can be maintained. 
     The following explanation is for the behavior of one specified MFP  100  among the plurality of MFPs  100  in the image forming system shown by  FIG. 1 . Each of the plurality of MFPs  100  in the image forming system shown by  FIG. 1  performs the behavior similar to the following explanation. 
     In the following explanations, portable terminal devices  200   a ,  200   b ,  200   c ,  200   d ,  200   e  and  200   f  correspond respectively to “portable terminal device A”, “portable terminal device B”, “portable terminal device C”, “portable terminal device D”, “portable terminal device E”, and “portable terminal device F” in user information table  121  shown in  FIG. 5 . 
     In  FIGS. 6, 7, 9 to 11, 17 to 19, 22, 24, 25, and 28 to 30 , parts of equipments which constitute the image forming system of  FIG. 1  are shown. 
     Each of ranges RA 1 , RA 2 , RA 3 , RA 4 , RA 11 , RA 12 , RA 21 , RA 22 , RA 23 , RA 31 , and RA 32  conceptually shows a range in which the communication is uninterrupted. As for the ranges, the radio waves attenuation due to the presence of obstacles or the like is not considered. Hence, the ranges are different from actual ranges. 
       FIG. 6  shows the first figure indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
     Referring to  FIG. 6 , user A carrying the portable terminal device  200   a  approaches MFP  100  as shown by arrow AR 1 , and each of MFP  100  and portable terminal device  200   a  is ready for communicating. MFP  100  begins to perform the direct wireless communication DW with portable terminal device  200   a . MFP  100  acquires necessary information from portable terminal device  200   a , and executes processes of the authentication for user A based on the acquired information. 
     At the time point when MFP  100  and portable terminal device  200   a  start the direct wireless communication DW, the MFP  100  does not perform direct wireless communication with portable terminal devices  200   b ,  200   c ,  200   d ,  200   e , and  200   f  other than the portable terminal device  200   a , and there is not a portable terminal device of a communication maintenance target. In the state in which there is not a portable terminal device of a communication maintenance target, MFP  100  sets the intensity of the radio waves at the minimum value. In this instance, the range in which the communication is uninterrupted is range RA 1  which is minimum. 
     The range in which the communication is uninterrupted means a range in which the intensity of the radio waves received by portable terminal device  200  which is radio waves emitted from wireless communication unit  122  is a level at which the direct wireless communication between MFP  100  and portable terminal device  200  can be maintained, when the portable terminal device  200  is present in the range. 
     Referring to  FIGS. 5 and 6 , when user. A was successfully authenticated, MFP  100  acquires information which relates to the connection area of portable terminal device A from user information table  121 , and sets connection area CA for portable terminal device  200   a  based on the acquired information. The connection area CA indicates a range as a reference for removing the portable terminal device as the communication maintenance target from communication maintenance targets. Here, it is supposed that the portable terminal device  200   a  is within the connection area CA. 
     Next, MFP  100  determines whether the portable terminal device  200   a  satisfies the specified condition or not. When MFP  100  determines the portable terminal device  200   a  satisfies the specified condition, MFP  100  regards the portable terminal device  200   a  as a communication maintenance target. The specified condition is a condition configured in view of whether it is going to be more likely that the target portable terminal device performs necessary communication with MFP  100  or not. 
     The specified condition may be that MFP  100  executed a job via portable terminal device A within a certain period from now (for example, within 3 months). In this instance, MFP  100  acquires the usage histories of user A from user information table  121 , and determines whether MFP  100  executed a job via portable terminal device A within a certain period from now or not, based on the usage histories. When a job was executed within the certain period from now, MFP  100  regards the portable terminal device  200   a  as a communication maintenance target. Because, portable terminal device  200  with high job execution frequency is supposed to be going to be more likely to perform necessary communication with that MFP  100 . 
     The certain period as an evaluation criterion may be able to be changed via operation panel  108 . For example, if a user executed a job within a period from the present to 24 hours ago, the portable terminal device of the user may be regarded as a communication maintenance target. For example, if a user executed a job within a period from the present to 3 days ago, the portable terminal device of the user may be regarded as a communication maintenance target. 
     The specified condition may be the number of data items which relate to user A stored in storage device  104 . In this instance, MFP  100  acquires information whether there is the box associated with the user A in storage device  104  or not, information whether the facsimile transmitting address of the user A is registered in storage device  104  or not, and information whether the mail address of user A is registered in storage device  104  or not, from user information table  121 . When the number of data items which relate to user A stored in storage device  104  is more than or equal to a predetermined number (two in this embodiment), MFP  100  regards portable terminal device  200   a  as a communication maintenance target. When storage device  104  stores numerous data which relate to the user as the owner of a portable terminal device  200 , the portable terminal device  200  is supposed to be going to be more likely to perform necessary communication with MFP  100 . 
     For example, when there is the box associated with user A in storage device  104 , storage device  104  registers the facsimile transmitting address of user A, and storage device  104  does not register the mail address of user A, the number of data items which relate to user A stored in storage device  104  is two, and the portable terminal device  200   a  is regarded as a communication maintenance target. When there is not a box associated with user A in storage device  104 , storage device  104  registers the facsimile transmitting address of user A, and storage device  104  does not register the mail address of user A, the number of data items which relate to user A stored in storage device  104  is one, and the portable terminal device  200   a  is not regarded as a communication maintenance target. 
     The specified condition may include the above mentioned both 2 conditions. In this instance, when at least one of the above mentioned 2 conditions is satisfied, MFP  100  may regard portable terminal device  200   a  as a communication maintenance target. 
     According to user information table  121  shown in  FIG. 5 , for each of portable terminal devices  200   a ,  200   b , and  200   c , there is the storing area associated with the user who possesses the portable terminal device in storage device  104 , the facsimile transmitting address of the user who possesses the portable terminal device is registered, and the user who possesses the portable terminal device executed a job on MFP  100  via the portable terminal device within a certain period from now. As for portable terminal device  200   d , the user who possesses the portable terminal device executed a job on MFP  100  via the portable terminal device within a certain period from now. Therefore, MFP  100  determines that it is going to be more likely that each of portable terminal devices  200   a ,  200   b ,  200   c , and  200   d  executes necessary wireless communication with MFP  100 , and regards each of portable terminal devices  200   a ,  200   b ,  200   c , and  200   d  as a communication maintenance target. 
     On the other hand, for each of portable terminal devices  200   e  and  200   f , there is not a storing area associated with the user who possesses the portable terminal device in storage device  104 , the facsimile transmitting address of the user who possesses the portable terminal device is not registered, and the user who possesses the portable terminal device did not execute a job on MFP  100  via the portable terminal device within a certain period from now. Therefore, MFP  100  determines the possibility of executing necessary wireless communication by each of portable terminal devices  200   e  and  200   f  with MFP  100  is low, and does not regard each of portable terminal devices  200   e  and  200   f  as a communication maintenance target. 
     Next, MFP  100  acquires information of the intensity of radio waves from portable terminal device  200   a  as a communication maintenance target. The information of the intensity of radio waves is the information of the intensity of radio waves emitted from wireless communication unit  122  and received by portable terminal device  200   a . Next, MFP  100  adjusts the local intensity of radio waves which wireless communication unit  122  emits, based on the acquired information of the intensity of radio waves, so that the intensity of radio waves emitted from wireless communication unit  122  and received by portable terminal device  200   a  is at the minimum level in which radio waves of the direct wireless communication between MFP  100  and portable terminal device  200   a  are not interrupted (an example of a predetermined range in which the direct wireless communication can be maintained). MFP  100  repeats the process for acquiring the information of the intensity of radio waves and the process for adjusting the intensity of radio waves which wireless communication unit  122  emits in the following manner, to adjust the intensity of radio waves which wireless communication unit  122  emits. 
     MFP  100  acquires the location information of portable terminal device  200   a  from portable terminal device  200   a  as a communication maintenance target. After that, the acquisition of the location information from portable terminal device  200   a  as a communication maintenance target is periodically performed. 
       FIG. 7  shows the second figure indicating the behavior of MFP  100 , according to the first embodiment of this invention.  FIG. 8  shows an example of the adjustment method for the intensity of radio waves emitted from wireless communication unit  122 , according to the first embodiment of this invention. 
     Referring to  FIGS. 7 and 8 , the range being over level LV 1  and less than level LV 2  shows the minimum level in which radio waves of direct wireless communication between MFP  100  and portable terminal device  200  are not interrupted. In other words, level LV 1  shows the lower limit of the predetermined range in which direct wireless communication can be maintained, and level LV 2  shows the upper limit of the predetermined range in which direct wireless communication can be maintained. 
     When MFP  100  acquires the first information of the intensity of radio waves from portable terminal device  200   a  as a communication maintenance target, it is often the case that the distance between MFP  100  and portable terminal device  200   a  is long and portable terminal device  200   a  exists outside the range RA 1 . Therefore, it is often the case that the intensity of radio waves firstly acquired by MFP  100  is weaker than level LV 1  at which direct wireless communication can be maintained, so that the direct wireless communication may be interrupted. When the acquired intensity of radio waves is weaker than level LV 1 , MFP  100  executes the beam forming at the intensity of radio waves which is adequately strong with respect to portable terminal device  200   a , so that the intensity of radio waves which portable terminal device  200   a  receives exceeds level LV 1 . The direction of the beam forming is configured based on the location information of portable terminal device  200   a.    
     When MFP  100  executes the beam forming with respect to portable terminal device  200   a , the intensity of radio waves in the direction of portable terminal device  200   a  becomes locally strong, so that the intensity of radio waves which portable terminal device  200   a  receives increases exponentially. The range in which the communication is uninterrupted expands locally in the direction of portable terminal device  200   a , changing from range RA 1  to range RA 2 . The intensity of radio waves which MFP  100  acquires at the second time is stronger than level LV 2 . When the acquired intensity of radio waves is stronger than level LV 2 , MFP  100  weakens the intensity of radio waves for the beam forming with respect to portable terminal device  200   a , so that the intensity of radio waves which portable terminal device  200   a  receives becomes less than level LV 2 . 
     When MFP  100  weakens the intensity of radio waves of the beam forming with respect to portable terminal device  200   a , the intensity of radio waves which portable terminal device  200   a  receives weakens. However, the intensity of radio waves which MFP  100  acquires at the third time is still stronger than level LV 2 . MFP  100  further weakens the intensity of radio waves of the beam forming with respect to portable terminal device  200   a , so that the intensity of radio waves which portable terminal device  200   a  receives becomes less than level LV 2 . 
     When MFP  100  further weakens the intensity of radio waves of the beam forming with respect to portable terminal device  200   a , the intensity of radio waves which portable terminal device  200   a  receives further weakens. Therefore, the intensity of radio waves which MFP  100  acquires at the fourth time exceeds level LV 1  and is less than level LV 2 . When the acquired intensity of radio waves exceeds level LV 1  and is less than level LV 2 , MFP  100  maintains the intensity of radio waves of the beam forming with respect to portable terminal device  200   a . The range in which the communication is uninterrupted in the direction of portable terminal device  200   a  narrows, changing from range RA 2  to range RA 3 . 
       FIG. 9  shows the third figure indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
     Referring to  FIG. 9 , the user B who possesses the portable terminal device  200   b  approaches MFP  100  as shown by arrow AR 2 , and MFP  100  and portable terminal device  200   b  are ready for communicating. MFP  100  starts direct wireless communication DW with portable terminal device  200   b , executes authentication process of user B, and sets connection area CA for portable terminal device  200   b . MFP  100  determines whether portable terminal device  200   b  satisfies the specified condition or not, and regards portable terminal device  200   b  as a communication maintenance target. In a manner similar to portable terminal device  200   a , MFP  100  adjusts the intensity of radio waves which wireless communication unit  122  emits (weakens the intensity of radio waves of the beam forming). In consequence, the range in which the communication is uninterrupted locally broadens in the direction of portable terminal device  200   b , changing from range RA 3  to range RA 4 . 
     Similarly, the user F who possesses the portable terminal device  200   f  approaches MFP  100  as shown by arrow AR 3 , and MFP  100  and portable terminal device  200   f  are ready for communicating. MFP  100  starts the direct wireless communication DW with portable terminal device  200   f , executes authentication process of user F, and sets connection area CA for portable terminal device  200   f . MFP  100  determines whether portable terminal device  200   f  satisfies the specified condition or not, and does not regard portable terminal device  200   f  as a communication maintenance target. MFP  100  does not adjust the intensity of radio waves which wireless communication unit  122  emits based on information indicating the intensity of radio waves received by portable terminal device  200   f  which is not a communication maintenance target. In consequence, direct wireless communication DW between MFP  100  and portable terminal device  200   f  is in a state in which that the wireless communication may be interrupted. The range in which the communication is uninterrupted remains range RA 4 . When portable terminal device  200   f  is present in range RA 4 , the intensity of radio waves which portable terminal device  200   f  receives is a level at which the direct wireless communication with MFP  100  can be maintained. 
     Direct wireless communication DW may be shut off for portable terminal devices  200   e  and  200   f  which are not communication maintenance targets on MFP  100  side, to avoid maintaining communication with portable terminal devices  200   e  and  200   f  when radio waves which portable terminal devices  200   e  and  200   f  which are not communication maintenance targets receive is weak. MFP  100  may beforehand receive a configuration of whether direct wireless communication DW is shut off with portable terminal devices  200   e  and  200   f  which are not to be communication maintenance targets or not, from an administrator of MFP  100  or the like. 
       FIG. 10  shows the fourth figure indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
     Referring to  FIG. 10 , user A carrying the portable terminal device  200   a  moves out of connection area CA, as shown by arrow AR 4 . When it is detected that portable terminal device  200   a  as a communication maintenance target exists out of connection area CA, MFP  100  removes portable terminal device  200   a  from communication maintenance targets, and turns off the beam forming toward portable terminal device  200   a . Herewith, direct wireless communication DW between MFP  100  and portable terminal device  200   a  is in the state in which the communication may be interrupted. In consequence, the range in which the communication is uninterrupted locally narrows, changing from range RA 4  to range RA 5 . MFP  100  may detect whether portable terminal device  200   a  exists out of connection area CA, based on the location information of portable terminal device  200   a , or based on the intensity of radio waves which portable terminal device  200   a  receives. 
       FIG. 11  shows the fifth figure indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
     Referring to  FIG. 11 , the user B who possesses portable terminal device  200   b  moves out of connection area CA, as shown by arrow AR 5 . When it is detected that portable terminal device  200   b  exists out of connection area CA, MFP  100  removes portable terminal device  200   b  from communication maintenance targets, and turns off the beam forming toward the portable terminal device  200   b . Herewith, direct wireless communication DW between MFP  100  and portable terminal device  200   b  is in the state in which the communication may be interrupted. In consequence, it is a state in which there is not a portable terminal device as a communication maintenance target, and MFP  100  sets the intensity of radio waves at the minimum value. The range in which the communication is uninterrupted changes from range RA 5  to range RA 1 . 
     In a state in which there is not a portable terminal device as a communication maintenance target, MFP  100  may stop radio waves (in other words, may set the minimum value of radio waves output as zero). Since portable terminal device  200   f  is not a communication maintenance target, the existence of direct wireless communication DW between MFP  100  and portable terminal device  200   f  and the location of portable terminal device  200   f  do not affect the intensity of radio waves which wireless communication unit  122  emits. 
     Connection areas with different ranges may be configured for portable terminal devices registered in user information table  121 . In this instance, MFP  100  may accept configurations of connection areas for portable terminal devices in the following manner, for example. 
       FIG. 12  schematically shows a screen for receiving configuration of a connection area displayed on a display unit DP in an operation panel  108 , according to the first embodiment of this invention. 
     Referring to  FIG. 12 , operation panel  108  includes a plurality of hardware keys HK, and display unit DP which is a touch panel. When the predetermined operation was received, MFP  100  displays a message for requesting a configuration of the connection area (a range in which connection with a terminal is available), the top view and the front view of MFP  100 , an “OK” key KY which is a software key, or the like on display unit DP. In the top view and the front view, back-and-forth, left-and-right, and up-and-down of the connection area centered on the MFP  100  (the distances from the location of the MFP to the boundary of connection area CA) are indicated by the arrows. When MFP  100  receives a pinch-in operation, a pinch out operation, or the like on display unit DP, MFP  100  enlarges or reduces the back, the forth, the left, the right, the up, or the down of the connection area in accordance with the received operation. When key KY is pressed, MFP  100  fixes the connection area, and registers it in association with the portable terminal device in user information table  121 . 
     The configuration of the connection area is set by the user of portable terminal device  200 , the administrator of MFP  100 , or the like. 
       FIGS. 13 and 14  show a flowchart indicating the behavior of MFP  100 , according to the first embodiment of this invention. 
     Referring to  FIG. 13 , when CPU  101  starts the direct wireless communication with a portable terminal device (S 101 ), CPU  101  determines whether the portable terminal device which is the communication partner is registered in user information table  121  or not (S 103 ). 
     At step S 103 , when the portable terminal device as the communication partner is registered in user information table  121  (YES at S 103 ), CPU  101  determines whether a connection area associated with the portable terminal device as the communication partner is registered in user information table  121  or not (S 105 ). 
     At step S 105 , when a connection area associated with the portable terminal device as the communication partner is registered in user information table  121  (YES at S 105 ), CPU  101  sets the registered connection area (S 107 ), and steps in the process of step S 111 . 
     At step S 105 , when a connection area associated with the portable terminal device as the communication partner is not registered in user information table  121  (NO at S 105 ), CPU  101  sets the default connection area centered on the MFP  100  (S 109 ), and steps in the process of step S 111 . 
     At step S 111 , CPU  101  determines whether the direct wireless connection with the portable terminal device as the communication partner is maintained or not (S 111 ). 
     At step S 111 , when the direct wireless connection with the portable terminal device as the communication partner is maintained (YES at S 111 ), CPU  101  receives the intensity of radio waves and the location information from the portable terminal device as the communication partner (S 113 ), and executes the communication maintenance target determining process which will be explained later (S 115 ). Next, CPU  101  determines whether the portable terminal device as the communication partner is regarded as a communication maintenance target or not, on the result of the communication maintenance target determining process (S 117 ). 
     At step S 117 , when the portable terminal device as the communication partner is regarded as a communication maintenance target (YES at S 117 ), CPU  101  turns on the beam forming toward the portable terminal device as the communication partner (S 119 ). Next, CPU  101  weakens the intensity of radio waves of the beam forming with respect to the portable terminal device as the communication partner at the minimum level at which the communication with the portable terminal device as the communication partner is uninterrupted (S 121 ), and steps in the process of step S 125  in  FIG. 14 . 
     When the portable terminal device as the communication partner is not registered in user information table  121  at step S 103  (NO at S 103 ), when the direct wireless connection with the portable terminal device as the communication partner is not maintained at step S 111  (NO at S 111 ), or when the portable terminal device as the communication partner is not regarded as a communication maintenance target at step S  117  (NO at S 117 ), CPU  101  does not perform the beam forming with respect to the portable terminal device as the communication partner (S 123 ), and terminates the process. 
     Referring to  FIG. 14 , at step S 125 , CPU  101  determines whether the portable terminal device as the communication partner moved out of the connection area or not (S 125 ). 
     At step S 125 , when the portable terminal device as the communication partner does not move out of the connection area (NO at S 125 ), CPU  101  determines whether the communication with the portable terminal device as the communication partner was shut off or not (S 129 ). 
     At step S 129 , when the communication with the portable terminal device as the communication partner is not shut off (NO at S 129 ), CPU  101  steps in the process of step S 125 . 
     When the portable terminal device as the communication partner moved out of the connection area at step S 125  (YES at S 125 ), or when the communication with the portable terminal device as the communication partner was shut off at step S 129  (YES at S 129 ), CPU  101  removes the portable terminal device as the communication partner from communication maintenance targets (S 127 ), and turns off the beam forming toward the portable terminal device as the communication partner (S 131 ). Next, CPU  101  determines whether there is another portable terminal device which is a communication maintenance target or not (S 133 ). 
     At step S 133 , when there is another portable terminal device as a communication maintenance target (YES at S 133 ), CPU  101  terminates the process. 
     At step S 133 , when there is not another portable terminal device as a communication maintenance target (NO at S 133 ), CPU  101  weakens the intensity of radio waves at the minimum value (S 135 ), and terminates the process. At step S 135 , CPU  101  may stop emitting radio waves. 
       FIG. 15  shows a subroutine of the communication maintenance target determining process (S 115 ) in  FIG. 13 . 
     Referring to  FIG. 15 , in the communication maintenance target determining process, CPU  101  acquires information relates to the user of the portable terminal device as the communication partner (S 151 ), and determines whether there is the job executed by MFP  100  within the certain period or not (S 153 ). 
     At step S 153 , when there is not the job executed by MFP  100  within the certain period (NO at S 153 ), CPU  101  determines whether there is the box or the facsimile transmitting address in MFP  100  or not (S 155 ). 
     At step S 153 , when there is the job executed by MFP  100  within the certain period (YES at S 153 ), or when there is the box or the facsimile transmitting address in MFP  100  at step S 155  (YES at S 155 ), CPU  101  regards the portable terminal device as the communication partner is a communication maintenance target (S 157 ), and returns to the main flowchart. 
     At step S 155 , when there is neither the box nor the facsimile transmitting address in MFP  100  (NO at S 155 ), CPU  101  does not regard the portable terminal device as the communication partner is a communication maintenance target (S 159 ), and returns to the main flowchart. 
     According to this embodiment, an MFP performs the beam forming toward a portable terminal device which is going to be more likely to perform necessary communication with the MFP. During the beam forming, the MFP weakens the intensity of radio waves of the beam forming with respect to the portable terminal device at the minimum level at which radio waves of the direct wireless communication with the portable terminal device are not interrupted. Herewith, the power consumption of the MFP can be reduced. 
     Further, it is determined whether a portable terminal device is going to be more likely to perform necessary communication with the MFP or not, based on whether the portable terminal device is registered or not, whether a job was executed via the portable terminal device recently or not, whether information which relates to the user of the portable terminal device is stored or not, whether the portable terminal device exists within the connection area, or the like. Hence, the target to which the beam forming executes can be suitably determined. 
     The beam forming is not executed for a portable terminal device with low possibility of performing necessary communication with the MFP, such as a portable terminal device which is not a communication maintenance target, a portable terminal device moved away from the MFP, a portable terminal device moved out of the connection area. Therefore, the intensity of radio waves which the wireless communication unit emits can be reduced, to reduce the power consumption. When the number of portable terminal devices with which MFP can simultaneously execute direct wireless communication is limited, the limited number of portable terminal devices can be effectively used. 
     When there is not a portable terminal device which is going to be more likely to perform necessary communication with the MFP, the intensity of radio waves which the wireless communication unit emits is set at the minimum value. Hence, the power consumption can be reduced. 
     The Second Embodiment 
     In this embodiment, the case in which MFP  100  works in conjunction with an entering/leaving room system will be explained. Connection areas are not set for users. 
       FIG. 16  shows an example of entering/leaving room table  321  stored in storage device  304  of a server  300 , according to the second embodiment of this invention.  FIG. 17  shows the first figure indicating the behavior of MFP  100 , according to the second embodiment of this invention. 
     Referring to  FIGS. 16 and 17 , the entering/leaving room table  321  records the entering/leaving room histories of the users of MFP  100 . The entering/leaving room histories include time and date of entering the room RM and time and date of leaving the room RM. The server  300  is an entering/leaving room system to perform the administration of entering/leaving room for the room RM, by using entering/leaving room table  321 . When the user of portable terminal device  200  enters the room RM from the door DR, the user performs the operation for entering the room by a method for moving his/her own ID card closer to a sensor (which is not shown in Figures) installed on the door DR, for example. The server  300  acquires the user ID via the sensor, and records the time and date of the entering the room of the user on entering/leaving room table  321 . When the user of portable terminal device  200  exits the room RM from the door DR, the user performs the operation for leaving the room by a method for moving his/her own ID card closer to a sensor SE, for example. The server  300  acquires the user ID via the sensor, and records the time and date of the leaving the room of the user on entering/leaving room table  321 . 
     MFP  100  acquires the entering/leaving room histories recorded in entering/leaving room table  321  from server  300 . MFP  100  can determine whether each of users is in the room or out of the room, based on which is later (newer), the time and date of the entering the room or the time and date of the leaving the room. MFP  100  may acquire the entering/leaving room histories for all the users recorded on entering/leaving room table  321  every time an arbitrary time elapses. MFP  100  may acquire the entering/leaving room history updated each time entering/leaving room table  321  is updated. 
     Referring to  FIG. 17 , all the users of portable terminal devices  200   a ,  200   b ,  200   c ,  200   d ,  200   e  and  200   f  are in the room RM, and all the portable terminal devices  200   a ,  200   b ,  200   c ,  200   d ,  200   e  and  200   f  exist in the room RM. MFP  100  are performing direct wireless communication DW with each of portable terminal devices  200   a ,  200   b ,  200   c ,  200   d ,  200   e  and  200   f . Portable terminal devices  200   a ,  200   b ,  200   c  and  200   d  are regarded as communication maintenance targets, and portable terminal devices  200   e  and  200   f  are not regarded as communication maintenance targets. 
     MFP  100  is performing the beam forming to each of portable terminal devices  200   a ,  200   b ,  200   c  and  200   d  which are communication maintenance targets, and the range in which the communication is uninterrupted is range RA 11 . The intensity of radio waves which each of portable terminal devices  200   a ,  200   b ,  200   c  and  200   d  receives is at the minimum level at which the radio waves of the direct wireless communication with MFP  100  are not interrupted, and the intensity of radio waves which each of portable terminal devices  200   e  and  200   f  receives is at a level at which the direct wireless communication with MFP  100  may be interrupted. 
       FIG. 18  shows the second figure indicating the behavior of MFP  100 , according to the second embodiment of this invention. 
     Referring to  FIG. 18 , the user A carrying the portable terminal device  200   a  performs the operation for leaving the room, and leaves the room RM as shown by arrow AR 11 . When MFP  100  detects that the user A left the room RM based on the information recorded on entering/leaving room table  321 , MFP  100  removes portable terminal device  200   a  from the communication maintenance targets, and turns off the beam forming toward portable terminal device  200   a . Herewith, the direct wireless communication DW between MFP  100  and portable terminal device  200   a  is in the state in which the communication may be interrupted. In consequence, the range in which the communication is uninterrupted narrows locally, changing range RA 11  to range RA 12 . 
       FIG. 19  shows the third figure indicating the behavior of MFP  100 , according to the second embodiment of this invention. 
     Referring to  FIG. 19 , the user B, the user C, the user D, the user E, and the user F, who possess the portable terminal devices  200   b ,  200   c ,  200   d ,  200   e  and  200   f  respectively perform the operation for leaving the room, and leave the room RM as shown by arrow AR 12 . When MFP  100  detects that all the users of portable terminal devices  200   b ,  200   c ,  200   d ,  200   e  and  200   f  which are the communication maintenance target left the room RM, MFP  100  removes portable terminal devices  200   b ,  200   c  and  200   d  from the communication maintenance targets, and turns off the beam forming toward portable terminal devices  200   b ,  200   c  and  200   d . Herewith, direct wireless communications DW between MFP  100  and portable terminal devices  200   b ,  200   c  and  200   d  are in the state in which the communications may be interrupted. In consequence, since there is not a portable terminal device as a communication maintenance target, MFP  100  sets the intensity of radio waves at the minimum value. The range in which the communication is uninterrupted is changed from range RA 12  to range RA 1 . 
     Since portable terminal devices  200   e  and  200   f  are not communication maintenance targets, whether user E or user F left the room RM or not does not affect the intensity of radio waves which wireless communication unit  122  emits. 
       FIGS. 20 and 21  show a flowchart indicating the behavior of MFP  100 , according to the second embodiment of this invention. 
     Referring to  FIG. 20 , at step S 103  in the flowchart shown in  FIG. 13 , when it is determined that the portable terminal device as the communication partner is registered in user information table  121  (YES at S 103 ), CPU  101  acquires the entering/leaving room histories for the user of the portable terminal device as the communication partner (S 201 ), and determines whether the user of the portable terminal device as the communication partner is in the room or not (S 203 ). 
     At step S 203 , when it is determined that the user of the portable terminal device as the communication partner is in the room (YES at S 203 ), CPU  101  steps in the process of step S 111  in the flowchart shown in  FIG. 13 . 
     At step S 203 , when it is determined that the user of the portable terminal device as the communication partner is out of the room (NO at S 203 ), CPU  101  does not perform the beam forming with respect to the portable terminal device as the communication partner (S 123 ), and terminates the process. 
     At step S 121  in the flowchart shown in  FIG. 13 , after weakening the intensity of radio waves of the beam forming with respect to the portable terminal device as the communication partner at the minimum level at which the communication with the portable terminal device as the communication partner is uninterrupted (S 121 ), CPU  101  steps in the process of step S 211  in  FIG. 21 . 
     Referring to  FIG. 21 , at step S 211 , CPU  101  acquires the entering/leaving room histories of the user of the portable terminal device as the communication partner, and determines whether the user of the portable terminal device as the communication partner left the room or not (S 211 ). 
     At step S 211 , when it is determined that the user of the portable terminal device as the communication partner left the room (YES at S 211 ), CPU  101  steps in the process of step S 127  in  FIG. 14 . 
     At step S 211 , when it is determined that the user of the portable terminal device as the communication partner did not leave the room (NO at S 211 ), CPU  101  determines whether the communication with the portable terminal device as the communication partner was shut off or not (S 129 ). 
     At step S 129 , when it is determined that the communication with the portable terminal device as the communication partner was not shut off (NO at S 129 ), CPU  101  steps in the process of step S 211 . 
     At step S 129 , when it is determined that the communication with the portable terminal device as the communication partner was shut off (YES at S 129 ), CPU  101  steps in the process of step S 127  in  FIG. 14 . 
     In this embodiment, the structures of the image processing system and the processes of MFP  100  other than the above described are similar to the first embodiment. The explanations are not repeated. 
     According to this embodiment, the beam forming is not performed with respect to a portable terminal device possessed by the user who left the room in which the MFP is installed. Hence, since the intensity of radio waves which the wireless communication unit emits can be reduced, the power consumption can be reduced. 
     Further, it is determined that it is going to be more likely that a portable terminal device performs necessary communication with the MFP or not, based on whether the user of the portable terminal device left the room or not, for example. Hence, the target to which the beam forming is performed can be suitably determined. 
     The Third Embodiment 
     According to this embodiment, the case in which MFP  100  does not have the beam forming function will be explained. 
     Here, it is assumed that MFP  100  does not perform direct wireless communication with each of portable terminal devices  200   b ,  200   c ,  200   d ,  200   e  and  200   f , other than portable terminal device  200   a , in a state in which there is not a portable terminal device as a communication maintenance target, and MFP  100  starts the direct wireless communication DW with portable terminal device  200   a  (the situation shown in  FIG. 6 ). In the situation, MFP  100  performs processes similar to the first embodiment, to regards portable terminal device  200   a  as a communication maintenance target. 
       FIG. 22  shows the first figure indicating the behavior of MFP  100 , according to the third embodiment of this invention. 
     Referring to  FIG. 22 , the MFP  100  acquires the information of the intensity of radio waves from portable terminal device  200   a  as the communication maintenance target. MFP  100  adjusts the intensity of radio waves which wireless communication unit  122  emits, so that the intensity of radio waves which portable terminal device  200   a  receives which is radio waves emitted from wireless communication unit  122  is at the minimum level at which radio waves of the direct wireless communication between MFP  100  and portable terminal device  200  are not interrupted, based on the acquired information of the intensity of radio waves. Since wireless communication unit  122  does not have a beam forming function, MFP  100  adjusts the intensity of radio waves in all directions from the MFP  100  without exception. MFP  100  repeats the acquiring process of the information of the intensity of radio waves, and the adjusting process of the intensity of radio waves which wireless communication unit  122  emits, in the following manner, to adjust the intensity of radio waves which wireless communication unit  122  emits. 
     MFP  100  acquires the location information of portable terminal device  200   a  from portable terminal device  200   a  as the communication maintenance target. After that, the location information is periodically acquired from portable terminal device  200   a  as the communication maintenance target. 
       FIG. 23  shows an example of the adjustment method of the intensity of radio waves emitted from wireless communication unit  122 , according to the third embodiment of this invention. 
     Referring to  FIGS. 22 and 23 , when the information of the intensity of radio waves was firstly acquired from portable terminal device  200   a  as the communication maintenance target, it is often the case that the distance between MFP  100  and portable terminal device  200   a  is long, and portable terminal device  200   a  exists outside of the range RA 1 . Therefore, it is often the case that the intensity of radio waves which MFP  100  acquired firstly is weaker than level LV 1  at which the direct wireless communication can be maintained, and the intensity of radio waves which MFP  100  acquired firstly is at a level at which the direct wireless communication may be interrupted. When the acquired intensity of radio waves is weaker than level LV 1 , MFP  100  strengthens the radio waves emitted from wireless communication unit  122  to a sufficiently large degree, so that the intensity of radio waves which portable terminal device  200   a  receives exceeds level LV 1 . 
     When the radio waves emitted from wireless communication unit  122  strengthens to a sufficiently large degree, the intensity of radio waves which portable terminal device  200   a  receives exponentially increases. The range in which the communication is uninterrupted is enlarged in all directions from the MFP  100  without exception, changing from range RA 1  to range RA 21 . The intensity of radio waves which MFP  100  secondary acquires is stronger than level LV 2  which is an arbitrary level which exceeds level LV 1 . When the acquired intensity of radio waves is stronger than level LV 2 , MFP  100  weakens the radio waves emitted from wireless communication unit  122 , so that the intensity of radio waves which portable terminal device  200   a  receives is less than level LV 2 . 
     When the radio waves emitted from wireless communication unit  122  weakens, the intensity of radio waves which portable terminal device  200   a  receives decreases. However, the intensity of radio waves which MFP  100  acquires at the third time is still stronger than level LV 2 . MFP  100  further weakens the radio waves emitted from wireless communication unit  122 , so that the intensity of radio waves which portable terminal device  200   a  receives is less than level LV 2 . 
     When the radio waves emitted from wireless communication unit  122  further weakens, the intensity of radio waves which portable terminal device  200   a  receives further decreases. Therefore, the intensity of radio waves which MFP  100  acquires at the fourth time exceeds level LV 1  and is less than level LV 2 . When the acquired intensity of radio waves exceeds level LV 1  and is less than level LV 2 , MFP  100  maintains the intensity of radio waves which wireless communication unit  122  emits. The range in which the communication is uninterrupted narrows in all directions from the MFP  100  without exception, changing from range RA 21  to range RA 22 . 
       FIG. 24  shows the second figure indicating the behavior of MFP  100 , according to the third embodiment of this invention. 
     Referring to  FIG. 24 , when the user B who possesses the portable terminal device  200   b  approaches MFP  100  as shown by arrow AR 21 , and MFP  100  and portable terminal device  200   b  are ready for communicating, MFP  100  performs processes similar to the first embodiment, to regard portable terminal device  200   b  as a communication maintenance target. In consequence, portable terminal devices  200   a  and  200   b  are communication maintenance targets. 
     When there are a plurality of portable terminal devices which are communication maintenance targets, MFP  100  adjusts the intensity of radio waves which wireless communication unit  122  emits, so that the intensity of radio waves received by a portable terminal device which receives the weakest radio waves emitted from wireless communication unit  122  (a portable terminal device farthest away from MFP  100 ) among the portable terminal devices which are communication maintenance targets is at the minimum level at which radio waves of the direct wireless communication with MFP  100  are not interrupted. 
     In  FIG. 24 , the distance between portable terminal device  200   b  and MFP  100  is longer than the distance between portable terminal device  200   a  and MFP  100 . Hence, the intensity of radio waves which portable terminal device  200   b  receives is weaker than the intensity of radio waves which portable terminal device  200   a  receives. Therefore, MFP  100  adjusts the intensity of radio waves which wireless communication unit  122  emits, so that the intensity of radio waves received by portable terminal device  200   b  which receives the weakest radio waves among portable terminal devices  200  as communication maintenance targets is at the minimum level at which radio waves of the direct wireless communication with MFP  100  are not interrupted. In consequence, the range in which the communication is uninterrupted are enlarged in all directions from the MFP  100  without exception, changing from range RA 22  to range RA 23 . 
     After user B approached MFP  100 , the user F who possesses the portable terminal device  200   f  approaches MFP  100  as shown by arrow AR 22 . When MFP  100  and portable terminal device  200   f  are ready for communicating, MFP  100  performs processes similar to the first embodiment, and does not regard portable terminal device  200   f  as a communication maintenance target. MFP  100  does not adjust the intensity of radio waves which wireless communication unit  122  emits, based on information indicating the intensity of radio waves received by portable terminal device  200   f  which is not a communication maintenance target. In consequence, direct wireless communication DW between MFP  100  and portable terminal device  200   f  is in the state in which the communication may be interrupted. The range in which the communication is uninterrupted remains range RA 23 . 
       FIG. 25  shows the third figure indicating the behavior of MFP  100 , according to the third embodiment of this invention. 
     Referring to  FIG. 25 , user A carrying the portable terminal device  200   a  moves out of connection area CA, as shown by arrow AR 23 . user B carrying the portable terminal device  200   b  moves out of connection area CA, as shown by arrow AR 24 . When MFP  100  detects that portable terminal device  200   a  and portable terminal device  200   b  exist out of connection area CA, MFP  100  removes portable terminal device  200   a  and  200   b  from communication maintenance targets. Herewith, direct wireless communication DW between MFP  100  and each of portable terminal devices  200   a  and  200   b  is in the state in which the communication may be interrupted. In consequence, there is not a portable terminal device which is a communication maintenance target, and MFP  100  sets the intensity of radio waves at the minimum value. The range in which the communication is uninterrupted narrows in all directions from the MFP  100  without exception, changing from range RA 23  to range RA 1 . 
     Since portable terminal device  200   f  is not a communication maintenance target, the existence of direct wireless communication DW between MFP  100  and portable terminal device  200   f , and the location of portable terminal device  200   f  do not affect the intensity of radio waves which wireless communication unit  122  emits. 
       FIGS. 26 and 27  show a flowchart indicating the behavior of MFP  100 , according to the third embodiment of this invention. 
     Referring to  FIG. 26 , at step S 117  in the flowchart shown in  FIG. 13 , when it is determined that the portable terminal device as the communication partner is regarded as a communication maintenance target (YES at S 117 ), CPU  101  weakens the intensity of radio waves which wireless communication unit  122  emits, so that the intensity of radio waves received by a portable terminal device which farthest away from MFP  100  among portable terminal devices which are communication maintenance targets is at the minimum level at which the radio waves of the direct wireless communication are not interrupted (S 301 ), and steps in the process of step S 125  in  FIG. 27 . 
     When it is determined that the portable terminal device as the communication partner is not registered in user information table  121  at step S 103  in the flowchart shown in  FIG. 13  (NO at S 103 ), when it is determined that the direct wireless connection with the portable terminal device as the communication partner is not maintained at step S 111  in the flowchart shown in  FIG. 13  (NO at S 111 ), or when it is determined that the portable terminal device as the communication partner is not regarded as a communication maintenance target at step S 117  in the flowchart shown in  FIG. 13  (NO at S 117 ), CPU  101  does not adjust the intensity of radio waves (S 303 ), and terminates the process. 
     Referring to  FIG. 27 , at step S 127  of the flowchart shown in  FIG. 13 , the portable terminal device as the communication partner is removed from communication maintenance targets (S 127 ). After that, CPU  101  determines whether another portable terminal device as a communication maintenance target exists or not (S 311 ). 
     At step S 311 , when it is determined that another portable terminal device as a communication maintenance target exists (YES at S 311 ), CPU  101  weakens the intensity of radio waves which wireless communication unit  122  emits, so that the intensity of radio waves which a portable terminal device farthest away from MFP  100  among portable terminal devices which are communication maintenance targets receives is at the minimum level at which radio waves of the direct wireless communication are not interrupted (S 313 ), and terminates the process. 
     At step S 311 , when it is determined that another portable terminal device as a communication maintenance target does not exist (NO at S 311 ), CPU  101  weakens the intensity of radio waves at the minimum value (S 315 ), and terminates the process. At step S 315 , CPU  101  may stop emitting radio waves. 
     According to this embodiment, the MFP weakens the intensity of radio waves which the wireless communication unit emits in all the directions from the MFP without exception at the minimum level at which radio waves of the direct wireless communication with a portable terminal device which is going to be more likely to perform necessary communication with the MFP are not interrupted. Herewith, power consumption of the MFP can be reduced. 
     The Fourth Embodiment 
     According to the embodiment, the case in which MFP  100  does not have the beam forming function and MFP  100  works in conjunction with an entering/leaving room system will be explained. Connection areas are not configured for users. 
       FIG. 28  shows the first figure indicating the behavior of MFP  100 , according to the fourth embodiment of this invention. 
     Referring to  FIG. 28 , all the users of portable terminal devices  200   a ,  200   b ,  200   c ,  200   d ,  200   e , and  200   f  are in the room RM, and all the portable terminal devices  200   a ,  200   b ,  200   c ,  200   d ,  200   e , and  200   f  exist in the room RM. MFP  100  are performing direct wireless communication DW with portable terminal devices  200   a ,  200   b ,  200   c ,  200   d ,  200   e , and  200   f . The portable terminal devices  200   a ,  200   b ,  200   c , and  200   d  are regarded as communication maintenance targets, and the portable terminal devices  200   e , and  200   f  are not regarded as communication maintenance targets. 
     MFP  100  adjusts the intensity of radio waves which wireless communication unit  122  emits, so that the intensity of radio waves which portable terminal device  200   c  (a portable terminal device farthest away from MFP  100 ) which receives the weakest intensity of radio waves receives among portable terminal devices  200   a ,  200   b ,  200   c , and  200   d  as communication maintenance targets is at the minimum level at which radio waves of the direct wireless communication with MFP  100  are not interrupted. The range in which the communication is uninterrupted is range RA 31 . 
     Since portable terminal device  200   e  which is not a communication maintenance target among portable terminal devices  200   e  and  200   f  is out of range RA 31 , the intensity of radio waves which portable terminal device  200   e  receives is at a level at which the direct wireless communication with MFP  100  may be interrupted. 
       FIG. 29  shows the second figure indicating the behavior of MFP  100 , according to the fourth embodiment of this invention. 
     Referring to  FIG. 29 , the user C who possesses the portable terminal device  200   c  performs the operation for leaving the room, and leaves the room RM as shown by arrow AR 31 . When MFP  100  detects the user C left the room RM based on the information recorded on entering/leaving room table  321 , MFP  100  removes portable terminal device  200   c  from communication maintenance targets. MFP  100  adjusts the intensity of radio waves which wireless communication unit  122  emits, so that the intensity of radio waves which portable terminal device  200   d  (a portable terminal device farthest away from MFP  100 ) which receives the weakest intensity of radio waves among portable terminal devices  200   a ,  200   b , and  200   d  as communication maintenance targets receives is at the minimum level at which radio waves of the direct wireless communication with MFP  100  are not interrupted. Since wireless communication unit  122  does not have beam forming function, MFP  100  adjusts the intensity of radio waves in all directions from the MFP  100  without exception. In consequence, the range in which the communication is uninterrupted is reduced in all directions from the MFP  100  without exception, changing from range RA 31  to range RA 32 . The direct wireless communication DW between MFP  100  and portable terminal device  200   c  is in the state in which the communication may be interrupted. 
       FIG. 30  shows the third figure indicating the behavior of MFP  100 , according to the fourth embodiment of this invention. 
     Referring to  FIG. 30 , the user A, a user B, a user D, a user E, and a user F who possess the portable terminal devices  200   a ,  200   b ,  200   d ,  200   e , and  200   f  respectively performs the operation for leaving the room, and leave the room RM as shown by arrow AR 32 . When MFP  100  detects portable terminal devices  200   a ,  200   b ,  200   d ,  200   e , and  200   f  left the room RM, MFP  100  removes portable terminal devices  200   a ,  200   b , and  200   d  from communication maintenance targets. In consequence, it is a state in which a portable terminal device which is a communication maintenance target does not exist, and MFP  100  sets the intensity of radio waves at the minimum value. The range in which the communication is uninterrupted narrows in all directions from the MFP  100  without exception, changing from range RA 32  to range RA 1 . The direct wireless communication DW between MFP  100  and portable terminal devices  200   a ,  200   b , and  200   d  is in the state in which the communication may be interrupted. 
     Since portable terminal devices  200   e  and  200   f  are not communication maintenance targets, leaving the room RM of user E and user F does not affect the intensity of radio waves which wireless communication unit  122  emits. 
       FIGS. 31 and 32  show a flowchart indicating the behavior of MFP  100 , according to the fourth embodiment of this invention. 
     Referring to  FIG. 31 , at step S 103  of the flowchart shown in  FIG. 13 , when it is determined that the portable terminal device as the communication partner is registered in user information table  121  (YES at S 103 ), CPU  101  acquires the entering/leaving room histories of the user of the portable terminal device as the communication partner (S 401 ), and determines whether the user of the portable terminal device as the communication partner is in the room or not (S 403 ). 
     At step S 403 , when it is determined that the user of the portable terminal device as the communication partner is in the room (YES at S 403 ), CPU  101  steps in the process of step S 111  in the flowchart shown in  FIG. 13 .
         when it is determined that the portable terminal device as the communication partner is not registered in user information table  121  at step S 103  (NO at S 103 ), when it is determined that the user of the portable terminal device as the communication partner is not in the room at step S 403  (NO at S 403 ), when it is determined that the direct wireless connection with the portable terminal device as the communication partner is not maintained at step S 111  in the flowchart shown in  FIG. 13  (NO at S 111 ), or when it is determined that the portable terminal device as the communication partner is not regarded as a communication maintenance target at step S 117  in the flowchart shown in  FIG. 13  (NO at S 117 ), CPU  101  does not adjust the intensity of radio waves (S 407 ), and terminates the process.       

     At step S 117  in the flowchart shown in  FIG. 13 , when it is determined that the portable terminal device as the communication partner is regarded as a communication maintenance target (YES at S 117 ), CPU  101  weakens the intensity of radio waves which wireless communication unit  122  emits, so that the intensity of radio waves a portable terminal device farthest away from MFP  100  receives among portable terminal devices which are communication maintenance targets is at the minimum level at which radio waves of direct wireless communication are not interrupted (S 405 ), and steps in the process of step S 411  in  FIG. 32 . 
     Referring to  FIG. 32 , at step S 411 , CPU  101  acquires the entering/leaving room histories of the user of the portable terminal device as the communication partner, and determines whether the user of the portable terminal device as the communication partner left the room or not (S 411 ). 
     At step S 411 , when it is determined that the user of the portable terminal device as the communication partner left the room (YES at S 411 ), CPU  101  steps in the process of step S 127  in  FIG. 14 . 
     At step S 411 , when it is determined that the user of the portable terminal device as the communication partner does not leave the room (NO at S 411 ), CPU  101  determines whether the communication with the portable terminal device as the communication partner was shut off or not (S 129 ). 
     At step S 129 , when it is determined that the communication with the portable terminal device as the communication partner is not shut off (NO at S 129 ), CPU  101  steps in the process of step S 411 . 
     At step S 129 , when it is determined that the communication with the portable terminal device as the communication partner was shut off (YES at S 129 ), CPU  101  steps in the process of step S 127  in  FIG. 14 . 
     After the portable terminal device as the communication partner was removed from communication maintenance targets at step S 127  of the flowchart shown in  FIG. 14  (S 127 ), CPU  101  determines whether another portable terminal device as a communication maintenance target exists or not (S 411 ). 
     At step S 411 , when it is determined that another portable terminal device as a communication maintenance target exists (YES at S 411 ), CPU  101  weakens the intensity of radio waves which wireless communication unit  122  emits, so that the intensity of radio waves a portable terminal device farthest away from MFP  100  receives among portable terminal devices which are communication maintenance targets is at the minimum level at which radio waves of the direct wireless communication are not interrupted (S 413 ), and terminates the process. 
     At step S 411 , when it is determined that another portable terminal device as a communication maintenance target does not exist (NO at S 411 ), CPU  101  weakens the intensity of radio waves at the minimum value (S 415 ), and terminates the process. At step S 415 , CPU  101  may stop emitting the radio waves. 
     According to this embodiment, MFP weakens the intensity of radio waves which the wireless communication unit emits in all directions from the MFP without exception, at the minimum level at which radio waves of direct wireless communication with a portable terminal device which is going to be more likely to perform necessary communication with the MFP are not interrupted. Herewith, power consumption of the MFP can be reduced. 
     Whether a portable terminal device is going to be more likely to perform necessary communication with the MFP or not is determined, based on whether a user of a portable terminal device left the room or not, for example. Therefore, the target of the beam forming can be suitably determined. 
     OTHERS 
     In the first to the fourth embodiments, when MFP  100  receives a predetermined operation (for example, a predetermined key pressing) on operation panel  108 , or when the NFC communication was established between a portable terminal device and operation panel  108 , MFP  100  may regard portable terminal device  200   e  or  200   f  which is not a communication maintenance target as a communication maintenance target, as long as there is connection availability. 
     In the first to the fourth embodiments, the wireless communication device (an emitter of radio waves) is MFP  100 , and the communication apparatus (a receiver of radio waves) is portable terminal device  200 . However, the wireless communication device (an emitter of radio waves) may be portable terminal device  200 , and the communication apparatus (a receiver of radio waves) may be MFP  100 . 
     In the second or the fourth embodiment, CPU  101  of MFP  100  may restart emitting radio waves by wireless communication unit  122 , when a user of any of a plurality of a portable terminal devices  200  enters the room RM after stopping emitting radio waves by wireless communication unit  122 . 
     The above mentioned embodiments can be combined appropriately. 
     According to this invention, a wireless communication device which can reduce the power consumption and a control program for such the wireless communication device can be provided. 
     The processes in the above-mentioned embodiments can be performed by software and a hardware circuit. A computer program which executes the processes in the above embodiments can be provided. The program may be provided recorded in recording media of CD-ROMs, flexible disks, hard disks, ROMs, RAMs, memory cards, or the like to users. The program is executed by a computer of a CPU or the like. The program may be downloaded to a device via communication lines like the internet. The processes explained in the above flowcharts and the description are executed by a CPU in line with the program. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustrated and example only and is not to be taken by way limitation, the scope of the present invention being interpreted by terms of the appended claims.