Abstract:
A flexible display element capable of being rolled up and unfurled, comprises a back plate covering a back side of the display element, wherein the back plate comes into contact with the back side of the display element when the display element is rolled up, and at least a central portion of the back plate is separated from the display element to support the display element in a flat shape when the display element is unfurled. Thus, the display element and the back plate can be rolled up and carried with a simple configuration of the display element and the back plate, and the display element can be supported in a flat shape when unfurled. Therefore, it is possible to provide a flexible display element having high portability, ease of rolling, and retention of flatness during periods of use.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display element, portable equipment, and an imaging device which have high portability, a high compactifying capability, and high operability. 
     2. Description of the Related Art 
     Numerous kinds of portable equipment using flexible display elements which can be reduced in size when carried have been proposed. For example, like a roll-up display disclosed in Japanese Patent Application Laid-Open No. H09-216465, some kinds of portable equipment enable viewing of images recorded by thermal heads. According to Japanese Patent Application Laid-Open No. H09-216465, a recording medium pulled out of the main body of equipment is flexible like paper and does not have flatness alone. Therefore, as is evident from the drawings of Japanese Patent Application Laid-Open No. H09-216465, according to the characteristics, the recording medium has to be held with both hands to keep the flatness. 
     As disclosed in Japanese Patent Application Laid-Open No. 2003-250074 and Japanese Patent Application Laid-Open No. 2003-274250, some kinds of portable equipment have flexible displays and have the following drawbacks: when the strength of a display is increased to keep the shape of the display pulled out of the main body of equipment, the strength becomes a resistance to rolling when the display is stored. Thus it is difficult to roll up the display. On the other hand, when the flexibility of the display is increased to facilitate rolling, the shape retention of the display decreases. In order to keep the flatness, it is necessary to hold a gripping portion on the opposite side of the main body of equipment, thus operability is hard to obtain. 
     Further, Japanese Patent Application Laid-Open No. 2000-19980 proposes a display body that is curved when pulled out (claim  1  and paragraph [0022] in Japanese Patent Application Laid-Open No. 2000-19980). A small curvature causes an insufficient strength and the curvature has to be increased to obtain a sufficient strength. As a result, a curved display may be viewed and the display may not have a designed aspect ratio. 
     Furthermore, Japanese Patent Application Laid-Open No. 2000-10086 and Japanese Patent Application Laid-Open No. H09-134132 propose display units that are surrounded by frames keeping the flatness of the display units. Since the frames cannot be rolled up, a problem arises in storing the frames. Thus such equipment is stored in a complicated manner and the size reduction is limited. 
     In Japanese Patent Application Laid-Open No. 2004-118803 and Japanese Patent Application Laid-Open No. 2004-109382, displays are just foldable and thus the degree of size reduction is smaller than that of a roll-up display. 
     As described above, in related art, numerous kinds of equipment using flexible display elements are proposed which are reduced in size when carried. However, all of the methods are defective in ease of rolling (compactifying capability) and retention of flatness (operability) during periods of use. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to propose a flexible display element, potable equipment, and an imaging device which have high portability, ease of rolling, and retention of flatness during periods of use. 
     In order to attain the object, a display element according to a first aspect of the invention is a flexible display element capable of being rolled up and unfurled, including a back plate covering the back side of the display element, wherein the back plate comes into contact with the back side of the display element when the display element is rolled up, and at least a central portion of the back plate is separated from the display element to support the display element in a flat shape when the display element is unfurled. 
     According to the display element of the first aspect of the invention, the display element and the back plate can be rolled up and carried with a simple configuration of the display element and the back plate, and the display element can be supported in a flat shape when unfurled. Thus it is possible to provide a flexible display element having high portability, ease of rolling, and retention of flatness during periods of use. 
     In order to attain the object, a portable equipment according to a second aspect of the invention is a portable equipment including a flexible display element capable of being rolled up and unfurled, which includes a back plate on the back side of the display element, wherein the back plate comes into contact with the display element when the display element is rolled up, and the back plate is bent such that at least a central portion of the back plate is separated from the display element due to a bend when the display element is unfurled, and the flatness of the display element is kept by a structure made up of the display element and the back plate when the display element is unfurled. 
     According to the portable equipment of the second aspect of the invention, the back plate is provided on the back side of the flexible display element. The back plate comes into contact with the display element when rolled up, and at least the central portion of the back plate is separated from the display element due to a bend (deformation) when unfurled. Since the strength of the display element is kept by the back plate, a sufficient strength can be obtained by the bend. Thus even in the presence of a large bend, the display element is not bent and a designed aspect ratio can be obtained on display. 
     In order to attain the object, a portable equipment according to a third aspect of the invention is a portable equipment including a flexible display element capable of being rolled up and unfurled, further including a back plate on the back side of the display element, wherein the back plate reduces a resistance to a rolling movement by removing a lateral pressure in the planar direction of the display element to decrease shape retention of the display element when the display element is rolled up, and applies a lateral pressure to the display element to keep the shape of the display element flat when the display element is unfurled. 
     According to the portable equipment of the third aspect of the invention, the back plate can obtain shape retention when the display element is pulled out, and can reduce a resistance when the display element is rolled up. The back plate applies a lateral pressure in contact with both sides of the display element when bent, and removes the lateral pressure when rolled up, and a clearance is generated between the back plate and at least one of the sides of the display element, thereby reducing a resistance when the display element is rolled up. 
     According to a portable equipment of a fourth aspect of the invention, in one of the second and third aspects, the back plate is V-shaped in cross section with the central portion separated from the display element due to a bend when the display element is unfurled. 
     The portable equipment of the fourth aspect of the invention enables the back plate to have a highly stable shape and facilitates processing and product inspection. 
     According to a portable equipment of a fifth aspect of the invention, in the second to fourth aspects, the back plate has a ridge member to make a shape with a plurality of ridges by a plurality of bent portions separate from the display element, so as to form a space surrounded by the display element and the back plate when the display element is unfurled. 
     According the portable equipment of the fifth aspect of the invention, the display element is unfurled and placed on a table and the like with higher stability. 
     According to the portable equipment of a sixth aspect of the invention, in the second to fourth aspects, the back plate has one end fixed on the back side of the display element. 
     According to the portable equipment of the sixth aspect of the invention, the back plate has one end fixed on the back side of the display element, thereby reducing rattling caused by unsteadiness during transportation. 
     In order to attain the object, an imaging device according to a seventh aspect of the invention is an imaging device including at least a taking lens and a shooting part, the imaging device further including: a main body substantially shaped like one of a cylinder and a polygon, and a display element stored in the main body when carried, and pulled out of the main body when used to display a photographed image or a reproduced image, wherein the display element has a flatness keeping mechanism for keeping flatness when the display element is pulled out, and the flatness keeping mechanism keeps a predetermined positional relationship and shape relative to the main body by applying a restraining force to the pulled out display element, and releases the restraining force when the display element is stored in the main body. 
     According to the imaging device of the seventh aspect of the invention, shooting is enabled when the main body is held with one hand and the display element is pulled out with the other hand. At this moment, since the shape of the display element is kept by the flatness keeping mechanism, an operation can be performed with one hand holding the main body. Further, the display element can be easily rolled up when stored. The display element is pulled out to the left or the right when viewed from the back side of the main body. Considering that the shooting part is operated with the right hand of a photographer it is preferable to pull out the display element to the left in view of operability. 
     According to an imaging device of an eighth aspect of the invention, in the seventh aspect, the flatness keeping mechanism is a back plate covering the back side of the display element, the back plate comes into contact with the back side of the display element when the display element is rolled up, at least a central portion of the back plate is separated from the display element to support the display element in a flat shape when the display element is unfurled, a pull-out slot for the display element on the main body is formed to have a shape which is substantially identical to a cross-sectional shape of the unrolled back plate, and to have a clearance formed on a portion facing a surface of the display element. 
     According to the imaging device of the eighth aspect of the invention, the clearance of the pull-out slot of the main body does not bring the surface of the display element into contact with the pull-out slot, thereby preventing scratches. Additionally, the bent portion of the back plate is not flattened by the pull-out slot and thus the positional relationship between the main body and the display element can be kept. When the main body is held, the shape of a base (near the pull-out slot of the main body) is kept even in the presence of an external force applied to the display element, thereby strongly keeping the integration with the main body. According to this imaging device, shooting can be performed with one hand holding the main body and the display element can be easily rolled up when stored. 
     According to an imaging device of a ninth aspect of the invention, in the seventh aspect, the flatness keeping mechanism is a back plate covering the back side of the display element, the back plate comes into contact with the back side of the display element when the display element is rolled up, and at least a central portion of the back plate is separated from the display element to support the display element in a flat shape when the display element is unfurled, a pull-out slot for the display element of the main body is formed to have a shape which is flattened by a predetermined amount from a cross-sectional shape of the unrolled back plate, and to have a clearance formed on a portion facing a surface of the display element. 
     According to the imaging device of the ninth aspect of the invention, the clearance of the pull-out slot of the main body does not bring the surface of the display element into contact with the pull-out slot, thereby preventing scratches. Further, the back plate is flattened by the pull-out slot to about a half, so that a resistance to a rolling movement can be reduced. Since the back plate is not completely flattened, it is possible to prevent the display element from easily shaking. 
     According to an imaging device of a tenth aspect of the invention, in the seventh aspect, the flatness keeping mechanism is a back plate covering the back side of the display element, the back plate comes into contact with the back side of the display element when the display element is rolled up, and at least a central portion of the back plate is separated from the display element to support the display element in a flat shape when the display element is unfurled, a pull-out slot for the display element of the main body is formed to have a shape which is flatter than a cross-sectional shape of the unrolled back plate, and to have a clearance formed on a portion facing a surface of the display element. 
     According to the imaging device of the tenth aspect of the invention, the clearance of the pull-out slot of the main body does not bring the surface of the display element into contact with the pull-out slot, thereby preventing scratches. Further, since the back plate is flattened by the pull-out slot, a resistant to a rolling movement is reduced. 
     According to an imaging device of an eleventh aspect of the invention, in the seventh aspect, the flatness keeping mechanism is a back plate covering the back side of the display element, the back plate comes into contact with the back side of the display element when the display element is rolled up, and at least a central portion of the back plate is separated from the display element to support the display element in a flat shape when the display element is unfurled, a pull-out slot for the display element of the main body is formed to have a shape which is substantially identical to a cross-sectional shape of the unrolled back plate, and to have a clearance expanding toward the center, which is formed on a portion facing a surface of the display element. 
     According to the imaging device of the eleventh aspect of the invention, the clearance of the pull-out slot of the main body does not bring the surface of the display element into contact with the pull-out slot, thereby preventing scratches. Additionally, the bent portion of the back plate is not flattened by the pull-out slot and thus the positional relationship between the main body and the display element can be kept. When the main body is held, the shape of a base (near the pull-out slot of the main body) is kept even in the presence of an external force applied to the display element, thereby strongly keeping the integration with the main body. According to this imaging device, shooting can be performed with one hand holding the main body and the display element can be easily rolled up when stored. Moreover, even when the display element is slightly bent, the clearance expanding toward the center prevents rubbing on the display surface, thereby preventing scratches. 
     A portable equipment of a twelfth aspect of the invention, in the second to sixth aspects, further includes a pull-out slot for the display element on the main body of the portable equipment, the pull-out slot being formed to have a shape which is substantially identical to a cross-sectional shape of the unrolled back plate, and to have a clearance formed on a portion facing a surface of the display element. 
     According to the portable equipment of the twelfth aspect of the invention, the clearance of the pull-out slot of the main body does not bring the surface of the display element into contact with the pull-out slot, thereby preventing scratches. Additionally, the bent portion of the back plate is not flattened by the pull-out slot and thus the positional relationship between the main body and the display element can be kept. When the main body is held, the shape of a base (near the pull-out slot of the main body) is kept even in the presence of an external force applied to the display element, thereby strongly keeping the integration with the main body. According to this portable equipment, shooting can be performed with one hand holding the main body and the display element can be easily rolled up when stored. 
     A portable equipment according to a thirteenth aspect of the invention, in the second to sixth aspects, further includes a pull-out slot for the display element on the main body of the portable equipment, the pull-out slot being formed to have a shape which is flattened by a predetermined amount from a cross-sectional shape of the unrolled back plate, and to have a clearance formed on a portion facing a surface of the display element. 
     According to the portable equipment of the thirteenth aspect of the invention, the clearance of the pull-out slot of the main body does not bring the surface of the display element into contact with the pull-out slot, thereby preventing scratches. Further, the back plate is flattened by the pull-out slot to about a half, so that a resistance to a rolling movement can be reduced. Since the back plate is not completely flattened, it is possible to prevent the display element from easily shaking. 
     A portable equipment according to a fourteenth aspect of the invention, in the second to sixth aspects, further includes a pull-out slot for the display element on the main body, the pull-out slot being formed to have a shape which is flatter than a cross-sectional shape of the unrolled back plate, and to have a clearance formed on a portion facing a surface of the display element. 
     According to the portable equipment of the fourteenth aspect of the invention, the clearance of the pull-out slot on the main body of the portable equipment does not bring the surface of the display element into contact with the pull-out slot, thereby preventing scratches. Further, since the back plate is flattened by the pull-out slot, a resistant to a rolling movement is reduced. 
     A portable equipment according to a fifteenth aspect of the invention, in the second to sixth aspects, further includes a pull-out slot for the display element on the main body of the portable equipment, the pull-out slot being formed to have a shape which is substantially identical to a cross-sectional shape of the unrolled back plate, and to have a clearance expanding toward the center, the clearance being formed on a portion facing a surface of the display element. 
     According to the portable equipment of the fifteenth aspect of the invention, the clearance of the pull-out slot of the main body does not bring the surface of the display element into contact with the pull-out slot, thereby preventing scratches. Additionally, the bent portion of the back plate is not flattened by the pull-out slot and thus the positional relationship between the main body and the display element can be kept. When the main body is held, the shape of a base (near the pull-out slot of the main body) is kept even in the presence of an external force applied to the display element, thereby strongly keeping the integration with the main body. According to this imaging device, shooting can be performed with one hand holding the main body and the display element can be easily rolled up when stored. Moreover, even when the display element is slightly bent, the clearance expanding toward the center prevents rubbing on the display surface, thereby preventing scratches. 
     An imaging device according to a sixteenth aspect of the invention, in the seventh to eleventh aspects, further includes a detecting device which detects a movement of the display element, wherein operation modes are switched in synchronization with the movement of the display element from a first position to a second position. 
     According to the imaging device of the sixteenth aspect of the invention, the operation modes can be switched between OFF and ON in synchronization with a change of the display element between a stored state and a pull-out state. Since the imaging device is turned on/off in response to the pulling out/storage of the display element, high operability can be obtained. 
     An imaging device according a seventeenth aspect of the invention, in the seventh to eleventh and sixteenth aspects, further includes convex portions provided on portions of the back plate, which are folded to both ends of a display screen. 
     According to the imaging device of the seventeenth aspect of the invention, the convex portions are provided on portions of the back plate, which are folded to the ends of a screen. Thus the convex portions act as spacers when the display element is rolled up, thereby preventing scratches and rubbing on the display screen of the display element. 
     An imaging device according to an eighteenth aspect of the invention, in the seventh to eleventh, sixteenth, and seventeenth aspects, further includes a rolling detecting switch disposed on a position making contact with a portion outside a display range of the display element when the display element is rolled up, on a roll-up shaft of the display element stored in the main body, wherein the rolling detecting switch turns off at least a part of display on a display part when the display element is rolled up. 
     According to the imaging device of the eighteenth aspect of the invention, when the display element is rolled up around the roll-up shaft, the rolling detecting switch is provided on a position making contact with a portion outside the display range, and at least one of the display and the power supply is turned off when the display element is rolled up, so that at least one of the power supply and the display can be automatically turned off. Thus it is possible to prevent a skip of power shutdown and excessive power consumption. 
     In order to attain the object, a portable equipment according to a nineteenth aspect of the invention includes a back plate on the back side of a flexible display element, the back plate being bent with a central portion separated from the display element due to a bend when the display element is unfurled, and is closer to the display element when the display element is stored than when the display element is unfurled, wherein the back plate includes a reflective surface on the display element side of the back plate, and light emitting elements between the reflective surface and the display element. 
     According to the portable equipment of the nineteenth aspect of the invention, the back plate that is bent when unfurled is provided on the back side of the flexible display element, wherein the reflective surface is provided on the inner surface of the back plate and the light emitting elements are provided between the reflective surface and the display element. Thus it is possible to provide a display element having high compactifying efficiency, in which a back plate can also act as a reflecting mirror of backlights. 
     According to a portable equipment of a twentieth aspect of the invention, in the nineteenth aspect, the light emitting elements are provided on an intermediate position of the display element and the reflective surface by means of an elastic member, and the light emitting elements can be rolled in contact with the display element when the display element is rolled up. 
     According to the portable equipment of the twentieth aspect of the invention, the light emitting elements are provided on the intermediate position between the display element and the reflective surface by means of the elastic member, thereby improving light emitting characteristics. 
     According to a portable equipment of a twenty-first aspect of the invention, in the twentieth aspect, the elastic member is a flexible printed board having an interconnection of the light emitting elements. 
     According to the portable equipment of the twenty-first aspect of the invention, the flexible printed board also acts as the elastic member. Thus the light emitting elements can be provided on the intermediate point with a simple configuration. 
     According to a portable equipment of a twenty-second aspect of the invention, in the nineteenth to twenty-first aspects, the back plate comes into contact with the display element when the display element is rolled up, and the back plate is ridged to have a plurality of bent portions separate from the display element due to bends when the display element is unfurled. 
     According to the portable equipment of the twenty-second aspect of the invention, more even backlights can be obtained. 
     According to the display element, portable equipment, and the imaging device of the present invention, the back plate is provided on the back side of the display element, which comes into contact with the back side of the display element when the display element is rolled up, and supports the display element in a flat shape by separating from the display element at its central portion, at least, when the display element is unfurled. Thus it is possible to provide a flexible display element, portable equipment, and an imaging device which have high portability, ease of rolling, and retention of flatness during periods of use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an outside drawing showing a display device including a flexible display element according to a first embodiment; 
         FIG. 2  is an explanatory drawing showing the internal configuration of the main body of the display device shown in  FIG. 1 ; 
         FIG. 3  shows a state in which the display element of the display device of  FIG. 1  is rolled up around a roll-up shaft; 
         FIG. 4  is a sectional view showing the main body of the display device shown in  FIG. 1 ; 
         FIGS. 5A to 5D  are sectional views showing the display element and a back plate shown in  FIG. 1 ; 
         FIG. 6  is a perspective view showing the back plate of the display device shown in  FIG. 1 ; 
         FIG. 7  is an explanatory drawing showing the configuration of a roll-up spring; 
         FIG. 8  is an outside drawing showing a display device including a flexible display element according to a second embodiment; 
         FIG. 9  is a perspective view showing the display element of the display device shown in  FIG. 8 ; 
         FIGS. 10A and 10B  are sectional views showing the display element and the back plate of the display device shown in  FIG. 8 ; 
         FIG. 11  is an enlarged view mainly showing the display element of the display device shown in  FIG. 8 ; 
         FIG. 12  is a sectional view showing the main body of the display device shown in  FIG. 8 ; 
         FIGS. 13A to 13C  are explanatory drawings showing a flexible display element according to a third embodiment; 
         FIG. 14  is an outside drawing showing a display device including a flexible display element according to a fourth embodiment; 
         FIG. 15  shows a state in which an operation part is provided on the roll-up shaft of the display device shown in  FIG. 14 ; 
         FIG. 16  shows a state in which the display element of  FIG. 14  is rolled up around the roll-up shaft; 
         FIG. 17  is an explanatory drawing showing a flexible display element according to a fifth embodiment; 
         FIG. 18  is a perspective view showing the display element of  FIG. 17 ; 
         FIG. 19  is a rear view showing the display element of  FIG. 18 ; 
         FIG. 20  is a sectional view showing a back plate shown in  FIG. 19 ; 
         FIG. 21  is a sectional view showing the display element and the back plate of  FIG. 18 ; 
         FIG. 22  is a perspective view showing the display device of  FIG. 17  in which the display element is stored in the main body of the display device; 
         FIG. 23  is a development for explaining that the back plate of  FIG. 17  is flattened; 
         FIG. 24  is a rear view showing the back plate of  FIG. 23 ; 
         FIG. 25  is a sectional view showing the display element and the back plate of  FIG. 24 ; 
         FIG. 26  is a front perspective view in which the same configuration as the display device is applied to an imaging device; 
         FIG. 27  is a rear perspective view showing the imaging device of  FIG. 26 ; 
         FIG. 28  is a perspective assembly drawing showing the imaging device of  FIG. 26 ; 
         FIG. 29  is a perspective view showing a display element and a back plate which are applied to the imaging device of  FIG. 26 ; 
         FIG. 30  is a perspective view showing a state in which the display element of  FIG. 29  is rolled up around a roll-up shaft; 
         FIG. 31  is an explanatory drawing showing an operation state of the imaging device of  FIG. 26 ; 
         FIG. 32  is an explanatory drawing showing a state in which the display element is pulled out of the main body of the imaging device shown in  FIG. 26 ; 
         FIG. 33  is a rear perspective view showing the imaging device of  FIG. 32 ; 
         FIG. 34  is an explanatory drawing showing an operation state of the imaging device of  FIG. 33 ; 
         FIG. 35  is a block diagram showing the configuration of the imaging device of  FIG. 26 ; 
         FIG. 36  is a flowchart showing an example of the operating procedure of the imaging device shown in  FIG. 26 ; 
         FIG. 37  is an outside drawing showing a display device including a flexible display element according to a sixth embodiment; 
         FIG. 38  is an explanatory drawing showing a state in which the display element is pulled out of the main body of the display device shown in  FIG. 37 ; 
         FIG. 39  is an explanatory drawing showing a motor for rolling and unrolling the display element of  FIG. 38 ; 
         FIG. 40  is a flowchart showing an example of the operating procedure of the display device shown in  FIG. 38 ; 
         FIG. 41  is a block diagram showing the configuration of the display device of  FIG. 38 ; 
         FIG. 42  is a block diagram showing a configuration in which the display device of  FIG. 38  is applied to an imaging device; 
         FIGS. 43A to 43D  are explanatory drawings showing the shapes of the pull-out slot of the display device shown in  FIG. 38 ; 
         FIG. 44  is a perspective view of a display element including a back plate having backlights; 
         FIGS. 45A and 45B  are sectional views showing the display element of  FIG. 44 ; 
         FIG. 46  is a block diagram showing the configuration of an imaging device including the display element of  FIG. 44 ; 
         FIG. 47  is a perspective view of a display element including a back plate having backlights according to another embodiment; 
         FIGS. 48A and 48B  are sectional views showing the display element of  FIG. 47 ; 
         FIG. 49  is a perspective view of a display element including a back plate having backlights according to another embodiment; 
         FIGS. 50A and 50B  are sectional views showing the display element of  FIG. 49 ; 
         FIGS. 51A to 51F  are explanatory drawings showing back plates according to another embodiment; 
         FIGS. 52A and 52B  are explanatory drawings showing a back plate according to another embodiment; and 
         FIGS. 53A and 53B  show the cross-sectional shapes of another embodiment of  FIGS. 52A and 52B  when rolled and unrolled. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following will describe preferred embodiments of a display element, portable equipment, and an imaging device of the present invention in accordance with the accompanying drawings. 
     First, a number of flexible displays (e.g., organic EL displays) including flexible display elements have been proposed in which a resin, and so on, is used as a base material instead of a glass of the related art. 
       FIG. 1  is an outside drawing showing a display device (portable equipment)  12  including such a flexible display element  10  according to a first embodiment. In  FIG. 1 , the strip-like display element  10  is pulled out of a cylindrical main body  14 .  FIG. 2  shows the internal configuration of the main body  14  and a developed state of a roll-up shaft  16  for rolling up the display element  10  and the unrolled display element  10 .  FIG. 3  also shows the roll-up shaft  16  and the display element  10  having been completely rolled around the roll-up shaft  16 . 
     As shown in  FIG. 4 , the main body  14  of  FIG. 1  is made up of a cylindrical body  14 A having open ends, and caps  14 B for closing the open ends of the cylindrical body  14 A. The roll-up shaft  16  is disposed between the caps  14 B so as to rotate via a bearing portion  14 C, and is urged in a rolling direction by a roll-up spring  18  (see  FIG. 7 ). Further, the state of the unrolled display element  10  is kept by a stopper (not shown). 
     As shown in  FIG. 5A , the display element is shaped like a thin plate in cross section. Portions B on the longitudinal ends of the display element  10  include the bent portions  20  substantially bent into U-shapes. On the back side of the display element  10 , a back plate  22  having a free shape (when an external force is removed) of  FIG. 6  is attached. The back plate  22  is formed by, as shown in  FIG. 5B , connecting flat portions  24  of portions C on the longitudinal ends of the display element via a curved portion  26 . By connecting the two flat portions  24  to the curved portion  26 , the flexibility of the flat portions  24  is restricted and the surfaces of the flat portions  24  are kept in parallel with each other. The flat portions  24  are fit into and combined with the bent portions  20  of the display element  10  shown in  FIG. 5A , so that a cross-sectional shape in  FIG. 5C  is obtained. At this moment, the flat portions  24  are pressed to the back side of the display element  10  by the bent portions  20  and the flat portions  24  are kept in parallel with each other as described above. Thus the overall display element  10  is kept flat and the display element  10  pulled out of the main body  14  independently keeps the flatness as shown in  FIG. 1  or  2 . 
     In this state, even when an attempt is made to bend the display element  10  to the direction along arrows A of  FIG. 2  (or in the opposite directions: in such a direction that the display element  10  is bent along the width), the display element  10  cannot be easily bent because a force of the back plate  22  is applied to keep the flatness. Therefore, the display device  12  can be used by holding the main body  14  only with one hand, without holding the display element  10 . 
     The following is an operation of rolling up the display element  10 . 
     When the display element  10  is rolled up, the back plate  22  is flattened at portions A of  FIG. 2  by the roll-up shaft  16  and the curved shape is corrected to a flat shape in cross section as shown in  FIG. 5D . Thus the two flat portions  24  are connected via a plane and the force keeping the flatness of the display element  10  is not applied. Therefore, the display element  10  can be easily bent to the direction along the arrows A (or in the opposite directions) of  FIG. 2  and can be easily rolled up around the roll-up shaft  16 . The display element  10  rolled thus is stored in the main body  14  as shown in  FIG. 4 . 
     According to the first embodiment, the flexible display element  10  can be used after being unrolled (pulled out) from the main body  14 . The unrolled display element  10  keeps its flat shape with the flatness retaining action of the back plate  22 . When the display device  12  is carried, the display element  10  can be stored in the main body  14  as described above. 
       FIG. 8  is an outside drawing showing a display device (portable equipment)  112  including a flexible display element  110  according to a second embodiment. The  FIG. 8  shows the state that the display element  110  is unrolled.  FIG. 9  shows the single unit configuration of the display element  110 . Over the opposite side of a display surface  110 A, convex beam members  126  are bonded as shown in  FIG. 11 . With this configuration, the flexible display element  110  alone can be bent in direction D (and in the opposite direction) of  FIG. 9  but cannot be bent in direction E (and in the opposite direction). 
     As shown in  FIG. 12 , a main body  114  is made up of a cylindrical body  114 A having open ends, and caps  114 B for closing the open ends of the cylindrical body  114 A. A roll-up shaft  116  is disposed between the caps  114 B so as to rotate via a bearing portion  114 C and is urged in a rolling direction by a roll-up spring  118 . Further, the state of the unrolled display element  110  is kept by a stopper (not shown). 
     A back plate  122  combined with the display element  110  has a free shape (when an external force is removed) of  FIG. 10A , and bent portions  124  are formed on both longitudinal ends of the display element. When the bent portions  124  are used to combine the back plate  122  with the display element  110  of  FIG. 9 , the back plate  122  has a curved shape in cross section as shown in  FIG. 10B . At this moment, from the state of  FIG. 110A , the back plate  122  is extended and combined with the display element, so that lateral pressures indicated by arrows B of  FIG. 10B  are applied from the back plate  122  in the width direction of the display element  110 . The lateral pressures are received by the beam members  126  bonded on the back side of the display element  110 , so that the display element  110  keeps the cross-sectional shape of  FIG. 10B . Thus a force for keeping the flat shape is generated on the flexible display element  110  having been pulled out of the main body  114  of  FIG. 8 . In this way, the display element  110  pulled out of the main body  114  independently keeps its flatness. Also, one of the bent portions  124  of the back plate  122  may be fixed on the back side of the display element  110 . 
     In this state, even when an attempt is made to bend the display element  110  to the direction along the arrows D and E of  FIG. 9  (or in the opposite directions), the display element  110  cannot be easily bent because a force of the back plate  122  is applied to keep the flatness. Therefore, the display device  112  can be used by holding the main body  114  only with one hand, without holding the display element  110 . 
     The following is an operation of rolling up the display element  110 . 
     As in the first embodiment, when the display element  110  is rolled up, the back plate  122  is flattened by the roll-up shaft  116  because the display element  110  is rolled up around the roll-up shaft  116 , and the curved shape of the back plate  122  is corrected to a flat shape. When the back plate  122  is flattened thus, the lateral pressures applied to the flexible display element  110  are released. Thus the display element  110  can be bent along the arrow D (or in the opposite direction). Therefore, the display element  110  is smoothly rolled up around the roll-up shaft  116 . The display element  110  rolled thus is stored in the main body  114  as shown in  FIG. 12 . 
     As described above, according to the second embodiment of the present invention, the flexible display element  110  is used after being pulled out from the main body  114  and the unrolled (pulled-out) display element  110  keeps its flat shape alone. When carried, the display element  110  can be rolled up and thus can be stored in the main body  114 . 
       FIG. 13A  shows a display device  212  including a flexible display element  210  according to a third embodiment.  FIG. 3  is a sectional view showing a back plate  222  combined with the display element  210 .  FIG. 13B  is a sectional view showing the rolled display element  210 . On the longitudinal ends of the back side of the display element  210 , protruding pins  228  are disposed at a predetermined spacing along the longitudinal direction. Further, on the longitudinal ends of the back plate  222 , long holes  230  are formed at the same spacing as the pins  228 . The long holes  230  are formed along a direction (width direction) orthogonal to the longitudinal direction. 
     When the back plate  222  is attached to the display element  210  by fitting the pins  228  over the long holes  230 , the long holes  230  press the pins  228  in the direction orthogonal to the longitudinal direction in the state of  FIG. 13A  where an external force is not applied to the back plate  222 . Thus lateral pressures are applied to the display element  210 . On the other hand, in  FIG. 13B  where the back plate  222  is flattened, the pressing forces are eliminated and thus the lateral pressures are released, so that the display element  210  can be rolled up.  FIG. 13C  is a rear view showing the display element  210  of the display device  212 . In  FIG. 13C , lateral pressures are applied to the display element  210 . 
     In this way, the display element  210  is integrated with the back plate  222  by applying lateral pressures from the longitudinal ends in the width direction, and a raised part is formed at the center of the back plate  222 . Thus the overall display device  212  has stereoscopic shape and is not easily bent even by a bending force, so that the display element  210  keeps the flat shape. 
       FIG. 14  is an outside drawing showing a display device  312  including a flexible display element  310  according to a fourth embodiment. The display element  310  is unrolled.  FIG. 15  shows the single unit configuration of the display element  310 . In  FIG. 15 , on the back side of the display element  310 , a back plate  322  indicated by broken lines is bonded on a bonding portion  330  shaded by diagonal broken lines. As shown in  FIG. 15 , a roll-up shaft  316  also acts as a main body having an operation part  332  and a power switch  334 . 
     The back plate  322  to be combined with the display element  310  is substantially V-shaped in its free shape (when an external force is removed). When the back plate  322  is combined with the display element  310 , the back plate  322  is extended from the V-shape as shown in  FIGS. 14 and 15 . At this moment, the back plate  322  is combined while being extended. Thus a folded end  336  on the opposite side from the bonding portion  330  applies a lateral pressure to the display element  310  and the lateral pressure is accepted by the stiffness of the display element  310 , so that the flatness of the display element  310  is kept and a force for keeping the flat shape is generated on a part unrolled from the roll-up shaft  316  of  FIG. 15 . With this configuration, the display element  310  unrolled from the roll-up shaft  316  independently keeps its flatness. 
     In this state, even when an attempt is made to bend the display element  310 , the display element  310  cannot be easily bent because a force of the back plate  322  is applied to keep the flatness. Therefore, the display device  312  can be used by holding the roll-up shaft  316  only with one hand, without holding the display element  310 . 
     The following is an operation of rolling up the display element  310 . 
     When the display element  310  is rolled up, rolling is performed from the side of the roll-up shaft  316  (main body) as shown in  FIG. 14 . Thus the back plate  322  is flattened by the roll-up shaft  316  and the curved shaped is corrected to a flat shape as in the first embodiment. The back plate  322  flattened thus releases the lateral pressure applied to the display element  310  and thus the display element  310  can be bent and smoothly rolled up around the roll-up shaft  316 . The display element  310  rolled thus is rolled up around the roll-up shaft  316  as shown in  FIG. 16 . 
     As described above, according to the fourth embodiment, the flexible display element  310  is used after being unrolled from the roll-up shaft  316 . The display element  310  can keep its flat shape alone and when carried, the display element  310  can be stored while being rolled up around the roll-up shaft  316 . Thus the display device  312  can have high portability and operability. Reference numeral  338  denotes a pull for unrolling the display element  310 . When the display element  310  is rolled up, the pull  338  acts as a holding portion that is pressed to the arc-shaped back plate  322  to keep the shape of the back plate  322 . 
       FIG. 17  is an outside drawing showing a display device  412  including a flexible display element  410  according to a fifth embodiment. In  FIG. 17 , the display element  410  is unrolled (pulled out) from a main body  414 .  FIG. 18  shows the single unit configuration of the display element  410 .  FIG. 19  shows the back side of the display element  410 .  FIG. 20  is a sectional view of a back plate  422 . In  FIGS. 18 and 19 , the display element  410  has a predetermined thickness. The back plate  422  has a plurality of notches  442  formed to prevent convex portions  440  formed on both end portions for applying lateral pressures from causing resistances when the display element  410  is rolled up. 
     In the configuration of the display element  410 , it is needless to say that as long as beam members  126  are bonded over the opposite side of a display surface as shown in  FIG. 9 , it is possible to prevent the display element  410  from being bent even by lateral pressures applied by the back plate  422  as shown in  FIG. 21 . Moreover, the configuration is not particularly limited as long as the display element  410  is designed to have strength against a bend to be resistant to the lateral pressures of the back plate  422 , thus the display element may have a flat shape. 
       FIG. 22  is an outside drawing showing the display element  410  rolled up around a roll-up shaft  416  of the main body  414 .  FIGS. 23 and 24  are developments for explaining the state of the display element  410  and the back plate  422  in the main body  414  at this moment. Since the display element  410  is rolled up around the roll-up shaft  416  of the main body  414 , the back plate  422  is crushed and flattened. Thus the lateral pressures for keeping the flatness of the display element  410  are not applied to the display element  410 . 
     The cross-sectional shape at this moment is illustrated in  FIG. 25 . Since the folded portions  440  of the back plate  422  are separated from both ends of the display element  410 , the lateral pressures are released.  FIGS. 23 and 24  show virtual shapes. When the display element  410  is unrolled as shown in  FIGS. 23 and 24 , the back plate  422  is bent and the lateral pressures are applied to the display element  410  (see  FIGS. 18 and 19 ). 
       FIG. 26  is a front perspective view in which the same configuration as the display device of the present invention is applied to an imaging device (digital camera)  500 .  FIG. 27  is a rear perspective view of the imaging device  500 . A main body  502  is substantially shaped like a partially cut square pole. In the rear view, a pull-out slot of the display element is formed on the left (the pull-out slot is closed by a lid  504  fixed on an end of the display element and thus is not shown in  FIGS. 26 and 27 ). The lid  504  has a pull  506  formed to pull out the display element. 
     A retractable flash  508  capable of protruding and retracting is provided on the top surface of a main body  502 , a taking lens  510  is provided at the front of the upper part of the main body  502 , a grip  512  is formed under the taking lens  510 , and a release button  514  is disposed near the upper end of the grip  512 . 
     Further, a zoom lever  515  is disposed on the upper part of the back of the main body  502 , a direction key  518  is disposed under the zoom lever  515 , selecting buttons  520 ,  522  and  524  are provided near the pull-out slot (not shown), and indications showing operations and functions corresponding to these buttons  520  to  524  are engraved beside the buttons. 
     The buttons  520 ,  522  and  524  have a plurality of functions. When the display element is pulled out, the names of the functions (e.g., ON and OFF in  FIG. 33 ) are displayed on the display element so as to be close to the buttons. By pressing the selecting buttons  520 ,  522  and  524  at this moment, the functions displayed on the display element are performed instead of the engraved functions. Although the display element  110  of  FIG. 8  is illustrated in the following explanation, the display elements of  FIGS. 1 to 25  are all applicable to the imaging device. 
       FIG. 28  is an assembly drawing showing the internal configuration of the imaging device  500 . The display element (flexible display)  110  is rolled up around a roll-up shaft  516  disposed in the lower part of the main body  502 , and a lens unit  526  is disposed in a space above the roll-up shaft  516 . On the lens unit  526 , a retractable flash unit  528  is disposed. A main substrate  530  is disposed on the back side of the imaging device and a battery (not shown) is stored in an expanded part at the front of the grip. 
     The rolled flexible display  110  is shaped like a cylinder as shown in  FIG. 30 . When the flexible display  110  is unrolled as shown in  FIG. 29 , the flat shape is kept by the actions of lateral pressures applied by the back plate. 
     When the imaging device  500  is used, as shown in  FIG. 31 , a user holds the pull  506  with the left hand and pulls out the display element  110  while holding the main body  502  with the right hand. The roll-up shaft  516  of the display element  110  is urged in the rolling direction by the roll-up spring  18  shown in  FIG. 7 . When the display element  110  is unrolled to a predetermined position, the roll-up shaft  516  is locked by a roll-up shaft locking mechanism  531  (see  FIG. 35 ) made up of a known latching/unlatching mechanism, and the imaging device  500  enters a state of  FIGS. 32 and 33 . In this state, the display element  110  is not rolled back even when the user moves the left hand off the pull  506 . When a rolling detecting SW  533  (see  FIG. 35 ) for detecting the rotation of the roll-up shaft  516  detects that the display element  110  has been completely pulled out of the main body  502 , power is supplied to an imaging circuit by the action of a rolling detecting circuit  535  (see  FIG. 35 ) of the main substrate  530 , and then the taking lens  510  protrudes from a retraction position to a shooting position shown in  FIG. 32 . Power is supplied thus when the display element  110  is completely pulled out, thereby increasing immediacy for the imaging device  500  applied to a camera. 
     Further, the retractable flash  508  pops up concurrently with the operation of the taking lens  510  and a light emitting portion  509  is exposed as shown in  FIG. 32 . Next, when the imaging circuit is activated and a live-view image is outputted, the live-view image of a subject is displayed on the display surface of the display element  110  as shown in  FIG. 33 , enabling framing and other operations for photo shooting. At this moment, the flat shape of the display element  110  is kept by the back plate  122  and the pull-out slot of the main body  502  restricts the positional relationship relative to the main body  502 . Thus the display element  110  can be independently stabilized in a state in which the main body  502  is held with one hand as shown in  FIG. 34 , and the positional relationship and the flat shape of  FIG. 34  can be kept even when an external force is applied. Therefore, the operations of the imaging device, i.e., shooting, reproduction, edition and so on can be performed with one hand having held the main body  502  without holding the display element  110 , so that operability improves when the imaging device  500  is applied to a camera. 
     When the display element  110  is stored in the main body  502 , in response to the pull  506  strongly pulled in a pulling direction from the state of  FIG. 32 , the roll-up shaft  516  having been locked by the roll-up shaft locking mechanism  531  is unlocked and the display element  110  is rolled up around the roll-up shaft  516 . 
     When the rolling detecting switch  533  for detecting the rotation of the roll-up shaft  516  detects that the display element  110  has been completely rolled up around the roll-up shaft  516 , the operation of the imaging circuit is stopped by the action of the control circuit of the main substrate  530 , the taking lens  510  is moved from the shooting position to the retraction position, the image device enters the state of  FIG. 26  (protected by a barrier), and then the power is turned off. Further, the flash  508  is also stored in the main body  502  concurrently with the retracting operation of the taking lens  510 . In this way, the power is turned off concurrently with the rolling movement of the display element  110 , so that an operation for turning off the power can be omitted and thus the inconvenience can be eliminated. Moreover, portability remarkably increases when the imaging device  500  is applied to a camera. 
       FIG. 35  is a block diagram showing the configuration of the imaging device  500 . 
     A diaphragm device  532  is disposed behind the taking lens  510  of the imaging device  500 , and a CCD  534  is disposed on the image forming position of the taking lens  510 . The overall operation of the imaging device  500  is controlled by a CPU  536 . The CPU  536  acts as a system controlling circuit which controls a camera system according to a predetermined program and also acts as an arithmetic device which performs various operations such as autoexposure (AE) operation, autofocus (AF) operation, and white balance (WB) adjustment operation. 
     A program run by the CPU  536 , kinds of data required for control, and so on are stored in a ROM  538  connected to the CPU  536 . CCD pixel defect information, kinds of constant/information about camera operations, and so on are stored in an EEPROM  540 . 
     A memory  544  connected to the CPU  536  via a bus  542  is used as the expansion area of the program and the arithmetic area of the CPU  536  and also used as a temporary storage area of image data and audio data. A storage part  546  is a temporary memory only for image data. 
     The release button  514  is an operation button for inputting an instruction to start shooting and is a two-step stroke switch which is made up of an S 1  switch turned on by a half press and an S 2  switch turned on by a full press. 
     The display element  110  is driven as an electronic view finder for displaying through images during shooting and is also driven as an image production monitor for displaying still images and moving images during reproduction. Further, the display element  110  is also used as a display screen for a user interface. Menu information and information about selected items and setting contents are displayed on the display element  110  when necessary. Moreover, image data stored in the storage part  546  is reduced and displayed as thumbnail images on the display element  110 . 
     The main body  502  has a medium socket  548  in which a recording medium  550  is loaded. The type of recording medium  550  is not particularly limited. Various media including xD-PictureCard, a semiconductor memory card typified by SmartMedia (trademark), a portable and compact hard disk, a magnetic disk, an optical disk, and a magneto-optical disk can be used. 
     The media controller  552  performs necessary signal conversion to pass input/output signals suitably for the recording medium  550  loaded in the medium socket  548 . 
     Further, the imaging device  500  includes a communication circuit  556  for connection to a personal computer and other peripheral equipment via a connector or an antenna  554 . Reference numeral  558  denotes a switch for turning on/off an image displayed on the display element  110 , and reference numeral  560  denotes a display element driving circuit for driving the display element  110 . Reference numeral  562  denotes a power supply circuit through which power is supplied to the CPU  536  from a power supply device  564  such as a battery and so on. 
     The following will discuss the camera function of the imaging device  500 . 
     Zoom control, focus control, and iris control are performed on the taking lens  510  and the diaphragm device  532  by an exposure control circuit  566 , a distance-measurement control circuit  568 , a zoom/retraction control circuit  570 , and a lens extension/retraction confirming circuit  572  which are controlled by the CPU  536 . 
     Light having passed through the taking lens  510  forms an image on the light-receiving surface of the CCD  534 . A number of photodiodes (light receiving elements) are arranged in a two-dimensional manner on the light receiving surface of the CCD  534 , and primary-color filters of red (R), green (G), and blue (B) are so disposed as to correspond to the photodiodes in a predetermined arrangement. Further, the CCD  534  has an electronic shutter function of controlling the charge storage time (shutter speed) of each photodiode. The CPU  536  controls the charge storage time in the CCD  534  through a timing generator  574 . Imaging elements of other types such as a MOS may be used instead of the CCD  534 . 
     A subject image formed on the light receiving surface of the CCD  534  is converted into signal charge by the photodiodes according to an amount of incident light. The signal charge having been accumulated in the photodiodes is read sequentially as voltage signals (image signals) corresponding to the signal charge based on a driving pulse applied from the timing generator  574  in response to an instruction of the CPU  536 . 
     Signals outputted from the CCD  534  are transmitted to an analog processing section, in which RGB signals of each pixel are sampled and held (correlated double sampling) before being amplified. After that, the signals are applied to an AD converter  576 . The RGB signals having been converted into digital signals by the AD converter  576  in a dot sequential manner are stored in an image display memory  580  through a memory control section  578 . 
     The RGB signals having been stored in the image display memory  580  are processed by an image processing circuit  582  according to an instruction of the CPU  536 . In other words, the image processing circuit  582  acts as an image processing device which includes a synchronization circuit (a processing circuit which interpolates a spatial displacement of a color signal in a color filter arrangement of a single-panel CCD and simultaneously converts the color signal), a white balance correction circuit, a gamma correction circuit, an edge correction circuit, and a luminance/color signal difference generation circuit. The image processing circuit  582  performs predetermined signal processing according to a command from the CPU  536  while using the image display memory  580 . 
     RGB image data inputted to the image processing circuit  582  is converted into a luminance signal and a color difference signal in the image processing circuit  582  and is subjected to predetermined processing such as gamma correction and so on. The image data having been processed in the image processing circuit  582  is stored in the storage part  546 . 
     When a photographed/reproduced image is outputted to the display element  110 , the image data is read from the storage part  546  and is transmitted to the display element driving circuit  560  through the bus  542 . The display element driving circuit  560  converts the inputted image data into a signal of a predetermined system for display (for example, an NTSC color combined video signal) (NTSC: National Television System Committee) and outputs the signal to the display element  110 . Further, a through image during shooting is displayed on the display element  110  from the image processing circuit  582  through the bus  542  and the display element driving circuit  560 . 
       FIG. 36  is a flowchart showing the control of a series of operations of the imaging device  500 . 
     When the rolling detecting switch  533  detects that the display element  110  has been completely pulled out (S 100 ), the display element driving circuit  560  is turned on (S 110 ). After that, the image display on/off switch  558  is turned on (S 120 ) and a mode dial (e.g., the selecting buttons  520 ,  522  and  524 ) is operated to select reproduction (S 130 ). At this moment, images recorded on the memory  544  and the storage part  546  are read and displayed on the display element  110  (S 140 ). When the mode dial is operated to select recording (S 130 ), an output image from the image processing circuit  582  is displayed on the display element  110  (S 150 ). Thereafter, at the completion of the operation of the imaging device  500 , the display element  110  is rolled back into the main body  502 . When the rolling detecting switch  533  detects that the display element  110  has been completely rolled up (S 160 ), the display element driving circuit  560  is turned off (S 70 ). The sequence of the imaging device  500  is completed thus. 
     As described above, when the imaging device  500  is applied to a camera, the configuration of  FIG. 34  eliminates the need for supporting the display element  110  with one hand while holding the main body  502  with the other hand, enabling one-hand shooting. A user can freely use the other hand (left hand in the present embodiment) for operations on the screen, the operations of a taking lens, and so on. Thus it is possible to achieve a camera having high operability without causing inconvenience. 
     Further, as shown in  FIG. 31 , by holding the main body  502  with one hand and pulling out the display element  110  with the other hand, the imaging device  500  can enter a shooting state. At this moment, the power is turned on and switching to a shooting mode is performed in synchronization with the rolling detecting switch  533 , shown in  FIG. 35 , for detecting rolling and a pulling-out detecting switch (not shown) for detecting the pulling out of the display element  110 , so that the imaging device  500  can enter the shooting state without the need for operating the power supply or switching modes. It is therefore possible to achieve a camera enabling excellent snapshots. 
       FIG. 37  is an outside drawing showing a display device  612  including a flexible display element  610  according to a sixth embodiment.  FIG. 37  shows a state in which a display element  610  is stored in a main body  614 , and  FIG. 38  shows a state in which the display element  610  is pulled out of the main body  614 . The present embodiment illustrates an example of an image player capable of displaying, on the display element  610 , image data stored in a built-in memory.  FIG. 39  shows the main part of the internal configuration of the image player. A rotating shaft  619  of a motor  618  is connected to a roll-up shaft  616 , and the display element  610  is pulled out and rolled up by electricity. Reference numeral  620  is a pull attached to an end of the display element  610  and also acts as a lid for closing a pull-out slot  615  of the main body  614 . 
     A series of operations of the display device  612  will now be described in accordance with the flowchart of  FIG. 40  and the block diagram of  FIG. 41  showing the image player. 
     When a power switch  622  is slid to the left (to the left when viewed from the display surface) in  FIG. 37  (S 200 ), it is detected that the power switch has been turned on, and an image display circuit  626  is turned on by a system controller  624  (S 210 ). Simultaneously, a driving circuit  628  is controlled to rotate the motor  618  of  FIG. 39  in a counterclockwise direction, and the display element  610  extends out along the arrow of  FIG. 38  (S 220 ). Thus the display screen can be observed and a menu screen stored in a built-in memory  630  is displayed on the display screen to receive various operations from operation buttons  632  (S 230 ). 
     Next, when the power switch is turned off (S 240 ), the motor  618  is rotated clockwise by the system controller  624 , and the display element  610  is rolled up around the roll-up shaft  616  (S 250 ). Simultaneously, the image display circuit is turned off (S 260 ) and the power switch waits for an input. The sequence is completed thus. In  FIG. 41 , reference numeral  634  denotes a connector connected to the system controller  624  via an input/output circuit  636 . The connector  634  is connected to external communication equipment, so that information is passed between the image player and the external communication equipment. 
       FIG. 42  is a block diagram showing an imaging device in which the display element  610  is rolled up by the rolling motor  618  by electricity. The configuration of the imaging device is substantially similar to that of the imaging device  500  shown in  FIG. 35 , except for the motor  618  and the driving circuit  628 . Thus the similar parts are indicated by the same reference numerals and the explanation thereof is omitted. Further, the series of operations in reproduction mode conforms to the sequence of  FIG. 40 . 
     As shown in  FIG. 38 , when the display element  610  and a back plate (not shown) are pulled out, the cross-sectional shape of the back plate is restricted by the shape of the pull-out slot  615  at the base of the main body  614 . 
       FIG. 43A  shows an example in which a pull-out slot  615 A is formed to have a shape which is substantially identical to the cross-sectional shape of the unrolled back plate. The pull-out slot  615 A formed thus can strongly keep the flatness of the unrolled display element  610 , so that the flatness can be more easily kept. On the front side of the display element  610 , only the outer periphery of the display element  610  and the edge of the pull-out slot  615 A come into contact with each other and the central portion of the display element  610  does not make contact with the pull-out slot  615 A because of a clearance. Thus the display surface is not rubbed and scratches can be prevented. 
       FIG. 43B  shows an example in which a pull-out slot  615 B is formed to have a shape which is flatter than the cross-sectional shape of the unrolled back plate in some small measure. Although the pull-out slot  615 B formed thus keeps the flatness of the unrolled display element  610  less than the pull-out slot  615 A of  FIG. 43A , a resistance upon rolling is low, so that the display element  610  can be easily stored. 
       FIG. 43C  shows an example in which a pull-out slot  615 C is formed to have a shape which is further flatter than the cross-sectional shape of the unrolled back plate. The pull-out slot  615 C formed thus reduces a force required for storing the display element  610 , so that the display element  610  can be frequently pulled out and stored with high operability. On the front side of the display element  610 ,  FIG. 43C  is similar to  FIG. 43A  in that only the outer periphery of the display element  610  and the edge of the pull-out slot  615 C come into contact with each other. However, since the clearance increases toward the central portion, the display surface is not rubbed and scratches can be prevented even when the display element  610  is somewhat bent. 
       FIG. 43D  shows a pull-out slot  615 D formed by combining the restricted back plate shape of  FIG. 43A  with the shape having the clearance of  FIG. 43C . 
     Since the back plate and the edge of the display element  610  are held through the pull-out slot  615 D, the base of the display element  610  is positioned relative to the main body  614  and the display element  610  keeps its protruding shape in a certain direction while keeping its flatness as shown in  FIG. 34 . With this configuration, without the need for holding the display element  610 , the display device  612  can be used as a display device or an imaging device by holding the main body  614  with one hand. 
       FIG. 44  is an outside drawing showing a display element and a back plate which are applied to the display devices of  FIGS. 1 ,  8  and  15  and the imaging device of  FIG. 26 . 
     As shown in  FIG. 44 , the display device of the present embodiment includes a flat display element  700  and a back plate  722  that is attached to the back side of the display element  700  and has a curved shape in cross section. The display element  700  has one end connected to a roll-up shaft  716  and the other end connected to a rod  718 , and thus the display element  700  is hardly bent by a force curving in the direction of an arrow  1  (or in the opposite direction). On the other hand, the display element  700  is easily bent by a force curving in the direction of an arrow  2  (or in the opposite direction), and thus the display element  700  can be rolled up around the roll-up shaft  716  and stored. The back plate  722  is curved and has a cross-sectional shape of  FIG. 45A  when unfurled. In this case, a clearance is generated between the display element  700  and the back plate  722  and increases toward the center. The display element  700  is a flexible LCD. Since transmitted light is necessary for viewing displayed images, as shown in  FIG. 44 , a plurality of LEDs  720  for backlighting are arranged around the center of the back plate  722  to transmit light at a distance from the back side of the display element  700 . A flexible printed board (flexible printed board for backlighting)  724  having the LEDs  720  is bonded to the back plate  722  and has one end connected to a backlight driving circuit  726  of  FIG. 46  (not shown in  FIG. 44 ) through the end of the back plate  722 . The light beams of the LEDs  720  are radially emitted as shown in  FIG. 45A . The back plate  722  has a reflective surface on which light beams emitted in respective directions are reflected to the display element  700  as shown in  FIG. 45A . Thus the LEDs  720  can be used as backlights. After rolled up, the display element  700  and the back plate  722  have a cross-sectional shape shown in  FIG. 45B . Since the back plate  722  substantially becomes flat in cross section, the display element  700  and the back plate  722  can be rolled up and stored in a small space. 
       FIG. 46  is a block diagram showing the case where the display element is applied to an imaging device. The configuration of the imaging device is substantially similar to that of the imaging device  500  shown in  FIG. 35 , except for the backlight LEDs  720  and the backlight driving circuit  726 . Thus the similar parts are indicated by the same reference numerals and the explanation thereof is omitted. 
       FIG. 47  is an outside drawing showing a display element  810  and a back plate  822  according to another embodiment in which light emitting elements are provided in two rows. 
     In a display device of the present embodiment, the display element  810  has one end connected to a roll-up shaft  816  and the other end attached to a rod  818 , so that the display element  810  is hardly bent in one direction and is easily bent in the other direction. Further, the display element  810  can be rolled up around the roll-up shaft  816  and stored. The back plate  822  is curved with two ridges  826  as shown in  FIG. 48A  and has a cross-sectional shape of  FIG. 48A  when unfurled. Moreover, a plurality of backlight LEDs  820  are arranged in two rows around the center of the back plate  822  to obtain more evenly transmitted light. A flexible printed board (flexible printed board for backlighting)  824  having the LEDs  820  is bonded to the back plate  822  and has one end connected to the backlight driving circuit  726  of  FIG. 46  through the end of the back plate  822 . The bend absorbing portions of the flexible printed board are bent in an unfurled state of  FIG. 47 . When the display element is rolled up and stored, the back plate  822  becomes flat and the spacing between the LEDs  820  is increased as shown in  FIG. 48B , so that dimensional changes are absorbed by the bent portions. The light beams of the LEDs  820  are radially emitted as shown in  FIG. 48A . The back plate  822  has a reflective surface on which the light beams emitted in respective directions are reflected to the display element  810  that is a flexible LCD as shown in  FIG. 48A , so that the LEDs are caused to act as backlights. After rolled up, the display element  810  and the back plate  822  have a cross-sectional shape shown in  FIG. 48B . The back plate  822  substantially becomes flat in cross section. Thus the display element  810  and the back plate  822  can be rolled up and stored in a small space. 
       FIG. 49  is an outside drawing showing a display element  910  and a back plate  922  according to another embodiment in which light emitting elements are arranged to emit light to the back side. 
     As shown in  FIG. 50A , the back plate  922  of the present embodiment is so bent as to have a second expanded portion  923  at the center of the back plate  922 . Further, backlight LEDs  920  are arranged around the center of the back plate  922  to emit light to the back plate  922 . A flexible printed board (flexible printed board for backlighting)  924  having the LEDs  920  is bonded to the back plate  922  with four bonded portions  924 A and has one end connected to the backlight driving circuit  726  of  FIG. 46  through the end of the back plate  922 . The flexible printed board  924  is bent with the LEDs  920  disposed at the intermediate position as shown in  FIG. 50A , and reflected light is emitted to the back side of the display element  910  through a reflective surface as shown  50 A. When unfurled, the back plate  922  is bent as shown in  FIG. 49 . When rolled up, the back plate  922  is flattened and is reduced in thickness as shown in  FIG. 50B , so that the display element  910  and the back plate  922  can be rolled up and stored in a small space. At this moment, the convex portions of the LEDs  920  facing the back side are stored in the second expanded portion  923  at the center of the back plate, so that the back plate  922  is not deformed. 
     The flexible printed board  924  does not always have to keep the shape of the display element  910 . Any configuration may be used as long as the flexible printed board  924  is bent and separated from the display element  910  when used and the flexible printed board  924 , when stored, comes into contact with or comes closer to the display element  910  than when used. 
       FIGS. 51A to 51D  show a back plate according to another embodiment. A back plate  1022  of  FIGS. 51A to 51C  has two high ridges  1026 . A back plate  1122  of  FIGS. 51D to 51F  has two ridges  1126  bent to be lower than the ridges  1026 . For convenience, reference numeral  10  denotes a display element. 
       FIGS. 52A and 52B  show a back plate according to still another embodiment. A back plate  1222  of  FIGS. 52A and 52B  does not have any ridges or is not substantially V-shaped but substantially has a recessed shape in cross section.  FIG. 53A  shows the cross-sectional shape of the unrolled display element and the unrolled back plate of  FIGS. 52A and 52B .  FIG. 53B  shows the cross-sectional shape of the rolled display element and the rolled back plate of  FIGS. 52A and 52B .