Abstract:
An electronic display device that allows the hierarchy or system to which the display screen belongs to be easily identified, without narrowing the display area of a plurality of screens constituting a director structure. In the display device, a plurality of key input screens form a director structure in association with each other. The directory structure includes first to fourth hierarchy levels. Respective key input screens are located at any of the hierarchy. Upon depression of a transition key in a basic screen belonging to the first hierarchy, the display screen is switched to one of key input screens belonging to the second hierarchy. The display device changes the display color according to the hierarchy to which the key input screen belongs in providing a display of a key input screen.

Description:
This application is based on Japanese Patent Application No. 10-168737 filed in Japan, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display device capable of color display used in setting the operation mode of a copy machine and the like. 
     2. Description of the Background Art 
     As a conventional display device used in entering the operational conditions of an apparatus, a display device that can set the operational condition through the manipulation of an operator according to the instruction provided on the display screen is known. For example, in a display device used in a copy machine, the copy mode such as the copy sheet size, the copy scaling factor, the copy density and the like is set by the operator selecting an appropriate item from the menu on the display screen or entering a numeric following the instruction displayed on the screen. More specifically, a directory structure is provided with a screen directed to set the copy mode such as the copy magnification rate or the copy density and a menu screen to derive an appropriate screen related to the copy mode set screen, associated with each other according to the function. The appropriate screens are sequentially displayed at the display device according to the directory structure. 
     FIG. 13 shows an example of the directory structure of screens provided displayed on a conventional device. Referring to FIG. 13, the first hierarchy corresponds to the basic screen. The second hierarchy corresponds to the scaling factor set screen, density set screen, and sheet set screen. Each screen of the second hierarchy is associated with the basic screen. The third hierarchy corresponds to a memory invoke screen  200  associated with the scaling factor set screen of the second hierarchy. The solid line in FIG. 13 implies the association of the connected screens. 
     When the copy mode is to be set using a screen of such a directory structure, first the basic screen of the first hierarchy is displayed. The screen of the second hierarchy can be displayed by depressing a transition key corresponding to a screen of a lower hierarchy in the basic screen. By depressing the transition key displayed in the scaling factor set screen of the second hierarchy, memory invoke screen  200  of the third hierarchy is displayed. FIG. 14 represents the display of memory invoke screen  200  of the third hierarchy at the display device. Memory invoke screen  200  includes display regions  201 - 203  to indicate the current working hierarchy for the operator. The screen format includes a region  202  of the scaling factor set screen within basic screen region  201 . The display shows memory invoke screen region  203  in scaling factor set screen region  202 . By confirming that display of display region  203  is displayed, the operator is aware that the current working screen corresponds to the third hierarchy. Thus, the hierarchical structure can be represented visually by displaying display regions  201 - 203 . 
     The number of items to be set at the time of manipulation increases as the function of the apparatus becomes more versatile. As a result, the number of screens to be displayed increases. There will be a greater number of hierarchies in the directory structure. Increase in the number of hierarchies renders the operation complicated. There was the case where the operator becomes confused as to what hierarchy level he/she is now working or what function of the copy mode he/she is now entering. 
     When the hierarchical structure is to be represented visually, a region indicating the higher hierarchy (display regions  201 - 202  of FIG. 14) must be provided. This induces the problem that the region to set the copy mode (display region  203  of FIG. 14) becomes smaller. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a display device superior in man-machine interface, capable of easily recognizing the hierarchy or system of the displayed screen without narrowing the region for display. 
     Another object of the present invention is to provide a display device superior in man-machine interface, capable of easily recognizing the association of the displayed screen with another screen without narrowing the region for display. 
     To achieve the above objects, a display device according to an aspect of the present invention includes a display unit selectively displaying a plurality of set screens to set a condition for image formation, and a control unit displaying a predetermined set screen of the plurality of set screens in the same color or same type of color, i.e. a similar color, at the display unit. 
     According to another aspect of the present invention, a display device includes a display unit to selectively display a plurality of set screens to set a condition for image formation, and a first key to alter a first set screen displayed at the display unit to a second set screen. The first key corresponds to a color associated with the second set screen. 
     According to a further aspect of the present invention, an image formation apparatus includes a display unit to selectively display a plurality of set screens to set a condition for image formation, a control unit to display a predetermined set screen of the plurality of set screens in the same color or similar color at the display unit, and an image forming device to form an image according to a set image formation condition. 
     According to the present invention, a display device superior in man-machine interface that allows the hierarchy or system pertaining to the displayed screen to be easily identified without reducing the display region. 
     According to the present invention, a display device superior in man-machine interface and that allows the association between the displayed screen and another screen to be easily identified without reducing the display region. 
    
    
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of the entire structure of a digital color copy machine in which a display device according to an embodiment of the present invention is applied. 
     FIG. 2 is a plan view of an operation panel unit of a digital color copy machine. 
     FIG. 3 is a block diagram showing a schematic structure of an operation panel unit. 
     FIG. 4 shows an example of a directory structure of a key input screen displayed at the display device of the present embodiment. 
     FIG. 5 shows an example of a basic screen displayed at the display device of the present embodiment. 
     FIG. 6 shows an example of a sheet set screen displayed at the display device of the present embodiment. 
     FIG. 7 shows an example of a scaling factor set screen displayed at the display device of the present embodiment. 
     FIG. 8 shows an example of a memory invoke screen displayed at the display device of the present embodiment. 
     FIG. 9 shows an example of a density set screen displayed at the display device of the present embodiment. 
     FIG. 10 shows an example of an application screen displayed at the display device of the present embodiment. 
     FIG. 11 shows an example of an insertion sheet set screen displayed at the display device of the present embodiment. 
     FIG. 12 shows an example of an insertion sheet medium set screen displayed at the display device of the present embodiment. 
     FIG. 13 shows a directory structure of a key input screen displayed at a conventional display device. 
     FIG. 14 shows a memory invoke screen displayed at a conventional display device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A display device according to an embodiment of the present invention will be described hereinafter with reference to the drawings. In the drawings, the same reference characters are allotted to the same or corresponding components. 
     First Embodiment 
     Referring to FIG. 1, a digital color copy machine includes an image reader  1  to read out an image of a document, and a copy unit  20  reproducing the read image. 
     Image reader  1  includes a scanner  10  reading the image of a document and converting the same into multi-bit electric signals, a motor  11  driving scanner  10 , an image processing unit  16  processing the multi-bit electric signal converted by scanner  10 , and a buffer  21  (FIFO memory) for synchronization to store the processed signal. Scanner  10  includes an exposure lamp  12  projecting a document mounted on a platen  15 , a rod lens array  13  collecting the reflected light from the document, and a contact-type CCD color image sensor  14  converting the gathered light into electric signals. Scanner  10  is driven by motor  11  during the document reading operation to move in the direction of the arrow (sub scanning direction) to scan the document placed on platen  15 . The image of the document irradiated with exposure lamp  12  is photoelectrically converted into multi-bit electric signals of the three colors of red, green and blue by CCD color image sensor  14 . The multi-bit electric signal is converted into gradation data of 8 bits for each of yellow (Y), magenta (M), cyan (C) and black (Bk) by a read out signal processing unit  16 . Gradation data of 8 bits are stored in synchronization buffer (FIFO memory)  21 . 
     Copy unit  20  includes a print head unit  22 , a photoconductor drum  41 , toner developing devices  35   a - 35   d , and a transfer drum  44 . Following a predetermined gradation correction (γ correction) on the gradation data of 8 bits input via synchronization buffer  21 , print head unit  22  D/A-converts the corrected image data to generate a laser diode driving signal. The semiconductor laser is modulated with the light emitting intensity according to this driving signal to output a laser beam. The laser beam output from print head unit  22  is reflected at a reflection mirror  23  to be directed onto photoconductor drum  41  that is driven in a rotating manner. Prior to this exposure, photoconductor drum  41  is irradiated with an eraser lamp  30  to be charged uniformly by a corona charger  31 . By the exposure of photoconductor drum  41  in a uniformly charged state, an electrostatic latent image is formed on photoconductor drum  41 . An appropriate one of cyan developing device  35   a , magenta developing device  35   b , yellow developing device  35   c  and black developing device  35   d  is selected to develop the electrostatic latent image on photoconductor drum  41 . 
     A copy sheet of an appropriate size is supplied from a sheet cassette  40  to transfer drum  44 . The copy sheet has its leading edge held by a chucking mechanism  45  so that the transfer position will not be shifted, and then wound around transfer drum  44 . The toner image developed on photoconductor drum  41  is transferred onto the copy sheet wound around transfer drum  44  by a transfer charger  36 . 
     This process of transferring a toner image onto the copy sheet is repeated for the four colors of yellow (Y), magenta (M), cyan (C) and black (Bk). Here, scanner  10  repeats a scanning operation in synchronization with the operation of photoconductor drum  41  and transfer drum  44 . Then, the copy sheet is detached from transfer drum  44  by a claw  37  to be discharged to a staple sorter  39  through a fixing device  38 . 
     An operation panel unit  50  is provided at the side of platen  15 . The user sets the copy mode through operation panel unit  50 . The digital color copy machine is controlled according to the set copy mode. For example, in staple sorter  39 , the copy sheet is discharged according to the discharge manner set via operation panel unit  50 . Here, the discharge manner includes the discharge of copy sheets continuously into one discharge tray, and the discharge of the same page into the same discharge tray, i.e., the stack manner. 
     Referring to FIG. 2, operation panel unit  50  includes a ten-key  54  to set the number of copies, the copy scaling factor, and the like, a print key  61  to designate the start of a copy operation, a LCD display unit  51 , and a reset button  56 . LCD display unit  51  includes a liquid crystal display device  52  and a touch switch  53  formed of a transparent member thereon. The screen displayed at liquid crystal display device  52  can be confirmed via touch switch  53  without parallax. 
     Referring to FIG. 3, microcomputer (referred to as CPU hereinafter)  55  provides control of operation panel  50  and also transmit the operation mode or print start indication set by the operator to copy unit  20  shown in FIG. 1 via a control line. A ROM  59  stores the display process program executed by operation panel unit  50 . A RAM  58  is backed up by a battery to store the copy conditions and the like set by the operator. A VRAM  57  stores the data of a screen to input various keys displayed on liquid crystal display device  52 . A MPX (multiplexer)  60  combines the data of the key input screen read out from VRAM  57  with the data of the copy mode read out from RAM  58  (for example, the number of copies or copy scaling factor) to provide the combined data to LCD controller  56 . LCD controller  56  provides data to liquid crystal display device  52  according to the data sent from CPU  55 . Liquid crystal display device  52  includes a back light that is turned ON/OFF by a switch  62  to provide a screen display according to a control signal sent from LCD controller  56 . 
     Touch switch  53  formed of a transparent member is provided on liquid crystal display device  52 . Touch switch  53  is divided into a total of 100 switches, ten in the vertical direction and ten in the horizontal direction. The position data of the switch depressed by the operator is sent to CPU  55 . CPU  55  recognizes the key depressed by the user out of the keys in the display screen of liquid crystal display device  52  according to the position data sent from touch switch  53  and the screen displayed on liquid crystal display device  52 . CPU  55  responds to the content of the recognized key to send a control signal to RAM  58 , VRAM  57  and LCD controller  56 , whereby the display screen of liquid crystal display device  52  is switched. 
     Referring to the directory structure of FIG. 4, a basic screen  100  is located at the first hierarchy. At the second hierarchy, a scaling factor set screen  130 , a density set screen  160 , a sheet set screen  120 , an application screen  170 , a finishing screen, and a document.copy screen are located. Each screen is associated with basic screen  100  of the first hierarchy. At the third hierarchy, a memory invoke screen  150 , an insertion sheet set screen  180 , a cover sheet set screen, an OHP insertion sheet set screen, a binding margin set screen, a book document set screen, and an erase set screen are located. Memory invoke screen  150  is associated with scaling factor screen  130  of the second hierarchy. The other key input screens are associated with application screen  170  of the second hierarchy. At the fourth hierarchy, an insertion sheet copy screen, an insertion sheet position set screen, and an insertion sheet medium set screen  190 , and multicopy screen are located. The insertion sheet copy screen, insertion sheet position set screen and insertion sheet medium set screen  190  are associated with insertion sheet set screen  180  of the third hierarchy. The multicopy screen is associated with the OHP insertion sheet set screen. 
     In FIG. 4, screens connected by solid lines are associated with each other. These associated screens are classified into respective types of systems over the first to fourth hierarchies. For example, scaling factor set screen  130  of the second hierarchy and memory invoke screen  150  of the third hierarchy are classified as a scaling factor set system  70 . Application screen  170  of the second hierarchy, insertion sheet set screen  180 , the cover sheet set screen, the OHP insertion sheet set screen, the binding margin set screen, the book document set screen, and the erase set screen of the second hierarchy, and the insertion sheet copy screen, the insertion sheet position set screen, the insertion sheet medium set screen, and the multicopy screen of the fourth hierarchy are classified as an application set system  73 . Furthermore, application set system  73  is classified as an insertion sheet set system  76  and an OHP insertion sheet set system  77  at the third and fourth hierarchies, respectively. Insertion sheet set system  76  includes insertion sheet set screen  180  of the third hierarchy, and the insertion sheet copy screen, the insertion sheet position set screen, and the insertion sheet medium set screen of the fourth hierarchy. An OHP insertion sheet set system  77  includes the OHP insertion sheet set screen of the third hierarchy and the multicopy screen of the fourth hierarchy. 
     Basic screen  100  of FIG. 5 is displayed when the power is turned on. Basic screen  100  is constituted by a selection key display section  101 , a message display section  102 , and a key display section  103 . Selection key display section  101  provides the display of a transition key to switch to a key input screen display corresponding to a copy mode. The copy mode is mainly classified into 4 groups according to the function. The transition key includes a basic key  105 , a document·copy key  106 , a finishing key  107 , and an application key  108 . When the user touches transition keys  105 - 108  with his/her finger, a key input screen corresponding to the transition key is displayed on liquid crystal display device  52 . When the user touches application key  108 , for example, application screen  170  (refer to FIG. 10) is provided on liquid crystal display device  52 . 
     Message display section  102  provides the display of the copy machine status such as “READY TO COPY” or “CURRENTLY COPYING”, also prompting messages such as “SELECT SHEET SIZE”, and the number of copies. 
     The mode set key and the transition key are displayed in key display section  103 . The mode set key functions to set the details of the copy mode. A copy mode corresponding to the depressed key is set. For example, this corresponds to the display of staple key  112  in FIG.  5 . In response to depression of staple key  112 , the mode is set to staple together the sheets on staple sorter  39 . The transition key functions to invoke another key input screen. 
     Referring to FIG. 5, basic screen  100  is a screen to set the basic copy mode. More specifically, the basic copy mode setting corresponds to the selection of the density, scaling factor, and the sheet for copy. A sheet key  109 , a scaling factor key  110  and a density key  111  which are transition keys are displayed in key display section  103 . In each of transition keys  109 - 111 , the details of the copy mode currently set are displayed. It is therefore not necessary to invoke a key input screen to set a copy mode in order to confirm the set status of the copy mode. For example, “automatic sheet” is displayed at sheet key  109 . This implies that a mode is set that selects from sheet cassette  40  a copy sheet of an appropriate size automatically from the scaling factor and the document size. Similarly, “×1.000” is displayed at scaling factor key  110 . This implies that the scaling factor is set to 1.000. “Automatic density” is displayed at density key  111 . This implies that a mode is set to automatically select a copy density according to the density of the image of the document. 
     CPU  55  detects the depression of any of transition keys  109 - 111  by the operator through tough key  53 , and provides a display of a key input screen corresponding to the sensed transition key at liquid crystal display device  52 . When an operator&#39;s input is not sensed for a predetermined period of time by touch key  53 , CPU  55  initializes the set copy mode to display a basic screen  100  at liquid crystal display device  52 . 
     Transition keys  106 - 111  of FIG. 5 are displayed in red. More specifically, the transition key is displayed in the color of the hierarchy pertaining to the key input screen displayed as a result of the transition key. 
     FIG. 6 represents a sheet set screen on liquid crystal display device  52  when sheet key  109  which is a transition key of basic screen  100  is depressed by the operator. In key display section  103  of sheet set screen  120 , sheet set section  121  is displayed in red. In sheet set section  121 , a mode set key  122  to set an “automatic sheet” mode, and mode set keys  123 - 126  to set the size of the copy sheet are displayed. In response to depression of mode set key  122  by the operator, the “automatic sheet” mode is set. In response to depression of mode set keys  123 - 126  to select a copy sheet by the operator, the “automatic sheet” mode is cancelled and a copy sheet corresponding to the depressed mode set key is selected. When basic screen  100  of FIG. 5 is subsequently displayed at liquid crystal display device  52 , a copy mode corresponding to the mode set key selected at sheet set screen  120  is displayed in sheet key  109 . 
     Referring to FIG. 7, the scaling factor set screen appears on liquid crystal display device  52  when scaling factor key  110  which is a transition key is depressed by the operator in basic screen  100 . In key display section  103  of scaling factor set screen  130 , a scaling factor set section  131  is displayed in red. 
     A mode set key  138  to set an “automatic scaling factor” mode, mode set keys  132 - 139  to set a predetermined scaling factor, and a memory key  140  for transition to a key input screen to invoke the scaling factor prestored in the memory by the operator are displayed in scaling factor set section  131 . Memory key  140  is a transition key, displayed in blue. In response to depression of mode set key  138  to set “automatic scaling factor”, the copy mode is set to a mode of automatically setting an appropriate scaling factor from the copy sheet size and the document size. In response to depression of mode set keys  132 - 139  to set a predetermined scaling factor, the copy mode is set to a scaling factor corresponding to respective mode set keys. Then, basic screen  100  shown in FIG. 5 is displayed on liquid crystal display device  52 . The scaling factor set at scaling factor set screen  130  is displayed in scaling factor key  110 . Upon depression of memory key  140  which is a transition key, memory invoke screen  150  of FIG. 8 is displayed at liquid crystal display device  52 . Memory invoke screen  150  is a screen to invoke the scaling factor selected by the operator and set the copy mode to that scaling factor. In key display section  103  of memory invoke screen  150 , scaling factor memory section  151  is displayed in blue. In scaling factor memory section  151 , scaling factor memory keys  152 - 154  which are mode set keys, and a preceding screen key  155  which is a transition key are displayed in scaling factor memory section  151 . Preceding screen key  155  is displayed in red. Upon depression of any of scaling factor memory keys  152 - 153 , the mode is set to the scaling factor predetermined by the operator. Then, the scaling factor preset by the user is displayed in scaling factor key  110  when basic screen  100  is displayed at liquid crystal display device  52 . Upon depression of preceding screen key  155 , scaling factor set screen  130  is displayed at liquid crystal display device  52 . 
     Upon depression of density key  111  in basic screen  100 , density set screen  160  shown in FIG. 9 is displayed. In key display section  103  of density set screen  160 , density set section  161  is displayed in red. A mode set key  162  to set the “automatic density” mode, and mode set keys  163  and  164  to manually set the density are displayed in density set section  161 . Upon depression of automatic density key  162 , the mode is set to “automatic density”. Upon depression of mode set keys  163  and  164  to manually set the density, the density of various levels such as “dark”, “slightly dark”, “normal”, “slightly light” and “light” are set. Then, when basic screen  100  is displayed at liquid crystal display device  52 , the display of “automatic density”, if set, or the density set manually appears in density key  111 . 
     Application screen  170  of FIG. 10 is displayed at liquid crystal display device  52  when application key  108  which is a transition key of basic screen  100  is depressed by the operator. In key display section  103  of application screen  170 , application set section  171  is displayed in red. In application set section  171 , transition keys  172 - 177  are displayed in blue to switch the key input screen display to set “cover sheet”, “insertion sheet”, “OHP insertion sheet”, “book document”, “binding margin”, “erase” copy modes. 
     FIG. 11 represents insertion sheet set screen  180  displayed at liquid crystal display device  52  when insertion sheet key  175  in application screen  170  is depressed by the operator. In key display section  103  of insertion sheet set screen  180 , insertion sheet set section  181  is displayed in blue. In insertion sheet set section  181 , a transition key  182  for transition to a key input screen to designate whether to copy or not on the insertion sheet, a transition key  183  for transition to a key input screen to set the position to insert the sheet, and a transition key  184  for transition to a key input screen to set the size of the insertion sheet are displayed in yellow. Then, an “OK” key  185  to display application screen  170  after ascertaining the setting of the insertion sheet mode, and a “cancel” key  186  to display application screen  170  after canceling the “insertion sheet” mode are displayed in blue. 
     Insertion sheet medium set screen  190  of FIG. 12 appears when the operator depresses transition key  184  for transition to a key input screen to set the size of the insertion sheet in insertion sheet set screen  180 . In key display section  103  of insertion sheet medium set screen  190 , insertion sheet medium set section  191  is displayed in yellow. Mode set keys  192 - 196  to select the size of the insertion sheet, and an “OK” key  197  ascertaining the insertion sheet size and displaying insertion sheet set screen  180  on liquid crystal display device  52  are displayed in insertion sheet medium set section  191 . “OK” key  197  is displayed in blue. Upon depression of mode set keys  192 - 196 , the mode is set to the insertion sheet corresponding to the depressed mode set key. 
     In the display device of the first embodiment, each hierarchy of the screen is displayed in an appropriate color. The operator can easily identify which hierarchy the currently working screen belongs to by just looking at the screen. The display area does not have to be reduced in area as in the conventional case. Therefore, operation error can be reduced. 
     Although the display hue of respective screens differs depending on the hierarchy in the present embodiment, the lightness of the displayed color of the screen can be made darker as the level of the hierarchy increases. Here, the hierarchy level refers to the first to fourth levels of hierarchy shown in FIG. 4, for example. The second hierarchy is higher in level than the first hierarchy. Since the operator can identify which hierarchy the currently worked screen belongs to by the lightness in addition to the hue, the level of the hierarchy can easily be identified. Alternatively, the hue does not have to be changed, and only the lightness altered for different hierarchy levels. 
     In the present embodiment, the color of the transition key displayed in the screen at liquid crystal display device  52  is set identical to that of the color of the destination key input screen display. Accordingly, the level of hierarchy to which transition is made can be identified at a glance by the depression of the relevant transition key. Therefore, operation error can be reduced. A similar effect can be obtained by displaying the transition key and the key input screen in related colors (for example similar colors), instead of displaying the transition key and the key input screen in the same color. 
     Second Embodiment 
     A display device according to a second embodiment of the present invention will be described hereinafter. In contrast to the display device of the first embodiment displaying the key input screen in different colors for respective hierarchies, the display device of the second embodiment sets a different display color for each system to which the display the key input screen belongs. The remaining elements are similar to those of the display device of the first embodiment. Therefore, description thereof will not be repeated. 
     The hierarchical structure of the key input screen displayed at liquid crystal display device  52  is as shown in FIG.  4 . Here, the system is defined by classifying the key input screen according to its function. More specifically, there are provided scaling factor set system  70 , density set system  71 , sheet set system  72 , application set system  73 , finishing set system  74 , and document·copy set system  75 . The color of the key input screen display is differentiated for every system. Specifically, scaling factor set screen  130  is displayed in red, density set screen  160  is displayed in blue, sheet set screen  120  is displayed in yellow, application screen  170  is set in green, finishing screen is set in orange, and the document-copy screen is displayed in pink. The screens belonging to the third hierarchy or the fourth hierarchy corresponding to the same system are displayed in the same color. 
     Sheet set screen  120  of FIG. 6 provides the display of sheet set section  121  in yellow. In scaling factor set screen  130  of FIG. 7, scaling factor set section  131  is displayed in red, and memory key  140  which is a transition key is displayed in red of a lightness lower in level than that of the red color of scaling factor set section  131 . In application screen  170  of FIG. 10, application set section  171  is displayed in green, and transition keys  172 - 177  are displayed in green of a darker shade than the green of application set section  171 . In insertion sheet set screen  180  of FIG. 11, insertion sheet set section  181  is displayed in green identical to the green of transition keys  172 - 177  in application screen  170 , whereas transition keys  182 - 184  are displayed in green of a lightness level lower than that of the green of insertion sheet set section  181 . Transition keys  185 - 186  are displayed in green identical to that of application set section  171  in application screen  170 . 
     In insertion sheet medium set screen  190  of FIG. 12, insertion sheet medium set section  191  is displayed in green identical to the green of transition keys  182 - 184  in insertion sheet set screen  180 , whereas transition key  197  is displayed in green identical to the green of insertion sheet set section  181  of insertion sheet set screen  180 . 
     Application set system  73  can be further subdivided with insertion sheet set system  76  and OHP insertion sheet set system  77 . In order to clearly show that these systems belong to application set system  73 , the color of the key input screen display belonging to insertion sheet set system  76  and OHP insertion sheet set system  77  can be set to a color associated with the display color of application screen  170  (for example, a similar color). 
     In the display device of the second embodiment, the screen is displayed in a different color for each system and the lightness of the color reduced in proportion to a higher level of hierarchy. Therefore, the operator can identify at a glance which system or which hierarchy level the currently worked screen belongs to. The operator can easily make a transit to the desired set screen, reducing any operational error. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.