Abstract:
Disclosed is an illumination device that makes it possible to improve the efficiency of the work of processing light-guide panels. Said illumination device is provided with: a light-guide panel ( 23 ) contained in a back chassis ( 21 ); and pressure members ( 31 ) that hold the light-guide panel ( 23 ) by applying pressure thereto. There are a plurality of pressure members ( 31 ), and at least one pressure member ( 31 ) is disposed on each side face ( 23   c  to  23   f ) of the light-guide panel ( 23 ), individually applying pressure to each of said faces  823   c  to  23   f ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to illumination devices and display devices. 
       BACKGROUND ART 
       [0002]    In display devices of the type known as liquid crystal display devices, the liquid crystal display panel that displays an image is non-luminous; thus, an illumination device is provided at the rear face side of the liquid crystal display panel (at the side of the liquid crystal display panel opposite from its display face surface), and the liquid crystal display panel is illuminated with the light from the illumination device. The illumination device provided at the rear face side of the liquid crystal display panel is called, for example, a backlight unit. 
         [0003]    Backlight units provided in liquid crystal display devices are roughly divided into a direct-lit type and an edge-lit type. 
         [0004]    Each type is structured, in brief, as follows. In a direct-lit backlight unit, a light source is arranged immediately behind the liquid crystal display panel (in a space facing the rear face of the liquid crystal display panel). The light emitted from the light source illuminates the liquid crystal display panel through optical sheets (such as a differ sheet, a lens sheet, and a polarizer sheet). 
         [0005]    On the other hand, in an edge-lit backlight unit, a light guide plate is arranged immediately behind the liquid crystal display panel, and a light source is arranged to face a predetermined side edge face of the light guide plate. The illuminating operation of an edge-lit backlight unit proceeds as follows. When the light source emits light, the light is introduced into the light guide plate through the predetermined side edge face thereof. The light introduced into the light guide plate is then repeatedly reflected internally so as to eventually exit from the light guide plate through the front face thereof (its face pointing to the liquid crystal display panel) as planar light and then illuminate the liquid crystal display panel through the optical sheets. 
         [0006]    The two types of backlight units are chosen to suit the purpose. Liquid crystal display devices dedicated to slim products adopt edge-lit backlight units, because these are advantageous to slimming down. 
         [0007]    In edge-lit backlight units, components such as a light guide plate and a light source are typically accommodated within an accommodation space inside a casing (accommodating container). Within the accommodation space, then, the light guide plate is held and positioned. 
         [0008]    As a method of positioning the light guide plate, for example, according to one conventionally known method, positioning protuberances are formed on a casing, and positioning recesses in which to fit the positioning protuberances are formed in the light guide plate, so that the protuberances on the casing are fitted in the positioning recesses (see, for example, Patent Document 1 listed below). 
         [0009]    According to another method, positioning pins are fitted within the accommodation space of the casing, and these positioning pins are fitted in positioning recesses in the light guide plate. 
         [0010]    In either case, conventionally, some processing for positioning needs to be applied to the light guide plate. 
       LIST OF CITATIONS 
     Patent Literature 
       [0011]    Patent Document 1: Japanese Patent Application Publication No. 2010-2745 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0012]    Certainly, positioning the light guide plate by the conventional methods mentioned above permits the light guide plate to be positioned satisfactorily; however, the processing of the light guide plate then requires an extra step of forming positioning recesses in the light guide plate. This increases the time required for the processing of the light guide plate. Thus, in cases where the light guide plate is positioned by the conventional methods, it is difficult to improve the efficiency of the processing of the light guide plate. 
         [0013]    Devised against the background discussed above, the present invention aims to provide an illumination device and a display device that allow improvement of the efficiency of the processing of a light guide plate. 
       Solution to Problem 
       [0014]    To achieve the above aim, according to a first aspect of the invention, an illumination device is provided with: a casing; a light guide plate accommodated in a casing and having a front face pointing toward an illuminated body, a rear face opposite from the front face, and a plurality of side edge faces contiguous with the front and rear faces; and a pressing member for pressing and thereby holding the light guide plate. The pressing member includes a plurality of pressing members which are arranged at least one at each of the plurality of side edge faces of the light guide plate, and the plurality of side edge faces of the light guide plate are each pressed individually by the corresponding at least one of the pressing members. 
         [0015]    In the illumination device according to the first aspect, as described above, in the structure where the light guide plate is held by being pressed by pressing members, at least one of the pressing members is arranged at each of the plurality of side edge faces of the light guide plate, and the plurality of side edge faces of the light guide plate are pressed individually by the pressing members, so that the light guide plate is held so as not to move (be displaced) in directions perpendicular to the thickness direction of the light guide plate; that is, the light guide plate is positioned in directions perpendicular to its thickness direction. This eliminates the need to separately provide positioning members for positioning the light guide plate in directions perpendicular to its thickness direction, and thus naturally eliminates the need to form in the light guide plate positioning recesses into which to fit those positioning members. The elimination of the need to form positioning recesses in the light guide plate shortens the processing time of the light guide plate accordingly, and this helps increase the efficiency of the processing of the light guide plate. 
         [0016]    In the illumination device according to the first aspect, it is preferable that the pressing members be formed of an elastically deformable cushion material. With this structure, even when the light guide plate is expansion-deformed under the influence of heat, the expansion-deformation of the light guide plate can be absorbed by the pressing members, and thus there is no need to previously reserve gaps between the plurality of side edge faces of the light guide plate and the pressing members respectively. Moreover, when the plurality of side edge faces of the light guide plate are pressed by their respective pressing members, the pressing members are in an elastically deformed (compression-deformed) state; thus even if the light guide plate is contraction-deformed, the pressing members undeform so as not to produce gaps between the plurality of side edge faces of the light guide plate and the pressing members respectively. In this way, wobbling of the light guide plate is suppressed. That is, incomplete positioning of the light guide plate is prevented, and the efficiency of the processing of the light guide plate is improved. 
         [0017]    In the illumination device according to the first aspect, it is preferable that two or more of the pressing members be arranged at each of the plurality of the side edge faces of the light guide plate. With this structure, the light guide plate can be held and positioned reliably. 
         [0018]    In the illumination device according to the first aspect, it is preferable that the light guide plate have a rectangular exterior shape as seen in a plan view from the direction facing the front face of the light guide plate, and that two of the pressing members be arranged at each of the plurality of the side edge faces of the light guide plate such that four corner portions of the light guide plate as seen in a plan view are pressed by the pressing members. That is, it is preferable that two of the pressing members be arranged at the side of each of four corner portions of the light guide plate as seen in a plan view. With this structure, in a case where a light guide plate having a rectangular exterior shape as seen in plan view is used, the light guide plate can be held and positioned in a well-balanced fashion. 
         [0019]    In the illumination device according to the first aspect, preferably, there may additionally be provided fixing members to which the pressing members are secured, and the fixing members may be fitted to the casing. With this structure, the pressing members can be fixed easily. Moreover, in a case where the pressing members need to be replaced for some reason, by removing the fixing members from the casing, the pressing members can be replaced easily. 
         [0020]    In the illumination device according to the first aspect, the pressing members may be secured to the casing, or the pressing members may be secured to the light guide plate. With this structure, the pressing members can be fixed easily. 
         [0021]    According to a second aspect of the invention, a display device is provided with: an illumination device according to the first aspect; and a display panel illuminated with the light from the illumination device. 
         [0022]    With the display device structured as described above, it is possible to improve the efficiency of the processing of the light guide plate. 
       Advantageous Effects of the Invention 
       [0023]    As described above, according to the present invention, it is possible to obtain an illumination device and a display device that allow improvement of the efficiency of the processing of a light guide plate 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]      FIG. 1  is an exploded perspective view of a display device incorporating an illumination device according to one embodiment of the invention (pressing members omitted); 
           [0025]      FIG. 2  is a sectional view, on a magnified scale, of part (around a light source) of an illumination device according to one embodiment of the invention; 
           [0026]      FIG. 3  is a plan view of an illumination device according to one embodiment of the invention as seen from the direction facing the front face of the light guide plate (optical sheets omitted); 
           [0027]      FIG. 4  is a sectional view, on a magnified scale, of part (around a pressing member) of an illumination device according to one embodiment of the invention; 
           [0028]      FIG. 5  is a perspective view of a pressing member in an illumination device according to one embodiment of the invention; 
           [0029]      FIG. 6  is a sectional view, on a magnified scale, of part (around a pressing member) of an illumination device according to a modified example of the invention; 
           [0030]      FIG. 7  is a diagram illustrating how pressing members are fixed in an illumination device according to a modified example of the invention; 
           [0031]      FIG. 8  is a diagram illustrating how pressing members are fixed in an illumination device according to a modified example of the invention; and 
           [0032]      FIG. 9  is a plan view of an illumination device according to a modified example of the invention as seen from the direction facing the front face of the light guide plate (optical sheets omitted). 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0033]    The structure of a display device incorporating an illumination device according to one embodiment of the present invention will be described below with reference to  FIGS. 1 to 5 . 
         [0034]    The display device is a liquid crystal display device and, as shown in  FIG. 1 , at least includes a liquid crystal display panel  10  which displays an image and a backlight unit  20  which is provided at the rear face side of the liquid crystal display panel  10  opposite from its display face side. The liquid crystal display panel  10  is an example of an “illuminated body” and a “display panel” according to the invention. The backlight unit  20  is an example of an “illumination device” according to the invention. 
         [0035]    The liquid crystal display device further includes a bezel BZ as a casing. The bezel BZ covers the liquid crystal display panel  10  and the backlight unit  20  from the display face side of the liquid crystal display panel  10 . 
         [0036]    The liquid crystal display panel  10  has a display area where an image is actually displayed and a non-display area which is the area outside the display area. In the display area of the liquid crystal display panel  10 , a plurality of pixels arrayed in a matrix are fabricated. 
         [0037]    The plurality of pixels are each driven via a switching device, a pixel electrode, a common electrode, etc. To avoid cluttering the drawings, however, no switching devices, pixel electrodes, or counter electrode are illustrated, and nor are any conductors or the like electrically connected to them. 
         [0038]    The switching device comprises a TFT (thin-film transistor), with the gate of the switching device connected to a gate line (scanning line) and the source of the switching device connected to a source line (data line). To the drain of the switching device, a pixel electrode is connected, and opposite the pixel electrode, a common electrode is arranged. Between the pixel electrode and the common electrode, liquid crystal (not shown) is held. Switching devices are provided one for each of the pixels, and so are pixel electrodes. On the other hand, a single common electrode is, as its name suggests, common to all the pixels. 
         [0039]    During display operation, based on a video signal, the optical property (light transmittance) of the liquid crystal is varied pixel-by-pixel. Specifically, in each pixel, a predetermined electric power is fed via the switching device to the pixel electrode so that an electric field is produced between the pixel electrode and the common electrode. The electric field produced between the pixel electrode and the common electrode changes the alignment of liquid crystal molecules and hence the transmittance with which light is transmitted through the liquid crystal. 
         [0040]    Thus, when the backlight unit  20  emits backlight and the backlight illuminates the rear face of the liquid crystal display panel  10 , the backlight is transmitted through the liquid crystal display panel  10  with varying transmittance from pixel to pixel. In this way, a desired image is displayed on the display face of the liquid crystal display panel  10 . 
         [0041]    Now, the structure of the liquid crystal display panel  10  and the backlight unit  20  will be described in more detail. 
         [0042]    As shown in  FIG. 1 , the liquid crystal display panel  10  at least includes two transparent substrates  11  and  12 . One transparent substrate  11  is called an active matrix substrate; the other transparent substrate  12  is often called a counter substrate because it is disposed opposite the transparent substrate  11  and is also called a color filter substrate. 
         [0043]    On a predetermined face of one transparent substrate  11 , switching devices and pixel electrodes are formed, and so are gate lines (scanning lines) and source lines (data lines) which are electrically connected to them. On a predetermined face of the other transparent substrate  12 , a common electrode is formed. On the predetermined face of the other transparent substrate  12 , in addition to the common electrode, color filters are also formed as necessary. The predetermined faces of the two transparent electrodes  11  and  12  are each covered with an alignment film (not shown) which can align liquid crystal molecules in a particular orientation. 
         [0044]    The two transparent substrates  11  and  12  are bonded together with a sealing member (not shown) in between such that their respective predetermined faces face each other. Between the two transparent substrates  11  and  12 , liquid crystal is sealed in. Thus, the liquid crystal is in a state held between the pixel electrodes and the common electrode (between the alignment film covering the predetermined face of one transparent substrate  11  and the alignment film covering the predetermined face of the other transparent electrode  12 ). 
         [0045]    The two transparent substrates  11  and  12  are given different exterior sizes such that the exterior size of the transparent substrate  11  is larger than the exterior size of the transparent substrate  12 . Accordingly, even though the two transparent substrates  11  and  12  are bonded together, an edge of the transparent substrate  11  does not coincide with an edge of the transparent substrate  12 , leaving part of the predetermined face of the transparent substrate  11  exposed out of the transparent substrate  12 . This exposed part of the predetermined face of the transparent substrate  11  is an area within the non-display area, and is used to electrically connect a driver (not shown) to the transparent substrate  11 . 
         [0046]    The faces of the two transparent substrates  11  and  12  opposite from their respective predetermined faces (liquid-crystal-side faces) are each laid with a polarizer sheet  13  which only transmits lightwaves oscillating in a particular direction. The two polarizer sheets  13  have their transmission axis directions displaced by 90 degrees from each other. 
         [0047]    As shown in  FIGS. 1 and 2 , the backlight unit  20  provided at the rear face side of the liquid crystal display panel  10  is of an edge-lit type, and at least includes a back chassis  21 , a reflective sheet  22 , a light guide plate  23 , an optical sheet  24 , and a light source module  25 . The back chassis  21  is an example of a “casing” according to the invention. 
         [0048]    The back chassis  21  is formed substantially in the shape of a box that is open at the liquid crystal display panel  10  side. That is, the back chassis  21  has a bottom portion and a side portion erect from around the edge of the bottom portion. The space surrounded by the bottom and side portions of the back chassis  21  serves as an accommodation space, and inside this accommodation space of the back chassis  21  are accommodated the reflective sheet  22 , the light guide plate  23 , the optical sheet  24 , and the light source module  25 . 
         [0049]    The reflective sheet  22  is placed on the inner surface of the bottom portion (the bottom face) of the back chassis  21 . Thus, the reflective sheet  22  permits the inner surface of the bottom portion (the bottom face) of the back chassis  21  to serve as a light reflecting surface. 
         [0050]    The light guide plate  23 , when light from the light source module  25  is introduced into it, emits it toward the liquid crystal display panel  10 . The light guide plate  23  has a front face  23   a,  a rear face  23   b  opposite from the front face  23   a,  and a plurality of side edge faces contiguous with the front and rear faces  23   a  and  23   b.  The light guide plate  23  is placed on the inner surface of the bottom portion (the bottom face) of the back chassis  21  with the reflective sheet  22  in between. The front face  23   a  of the light guide plate  23  points to the liquid crystal display panel  10 , and the rear face  23   b  of the light guide plate  23  points to the bottom portion of the back chassis  21 . 
         [0051]    Thus, the front face  23   a  of the light guide plate  23  serves as a light exit face through which the light introduced into the light guide plate  23  (the light from the light source module  25 ) is emitted toward the liquid crystal display panel  10 . On the other hand, the rear face  23   b  of the light guide plate  23  does not serve as a light exit face because it is covered by the reflective sheet  22 . 
         [0052]    As seen in a plan view (see  FIG. 3 ) from the direction facing the front face  23   a  of the light guide plate  23 , the exterior shape of the light guide plate  23  (the shape of the front and rear faces  23   a  and  23   b  as seen in a plan view) is rectangular without any protrusions or recesses. That is, the light guide plate  23  has four side edge faces  23   c  to  23   f  each formed as a flat surface (a substantially flat surface having no intentionally formed protrusions or recesses). Of the four side edge faces  23   c  to  23   f,  the side edge face  23   c  serves as a light entrance face which is struck by the light from the light source module  25 . Thus, through the side edge face  23   c  of the light guide plate  23 , the light from the light source module  25  is introduced into the light guide plate  23 . 
         [0053]    The side edge faces  23   c  and  23   d  of the light guide plate  23  are faces that point in opposite directions and that are parallel to the longer-side direction (X direction) of the light guide plate  23  as seen in a plan view. Likewise, the side edge faces  23   e  and  23   f  of the light guide plate  23  are faces that point in opposite directions and that are parallel to the shorter-side direction (Y direction) of the light guide plate  23  as seen in a plan view. 
         [0054]    The optical sheet  24  shown in  FIGS. 1 and 2  includes a diffuser sheet, a lens sheet, etc., and is placed on the front face (light exit face)  23   a  of the light guide plate  23 . The optical sheet  24  thus diffuses, condenses, and otherwise modifies the light emanating from the front face (light exit face)  23   a  of the light guide plate  23 . 
         [0055]    The light source module  25  generates the light (the light introduced into the light guide plate  23 ) from which backlight is produced, and is arranged at the side edge face  23   c  (light entrance face) of the light guide plate  23 . There is no particular restriction on the number of light source modules  25  used. For example, though not illustrated, another light source module  25  may be added and arranged at the side edge face  23   d  of the light guide plate  23 . In other words, in addition to the side edge face  23   c  of the light guide plate  23 , the side edge face  23   d  may also be made to function as a light entrance face. 
         [0056]    The light source module  25  has a structure in which a plurality of LEDs  27  are mounted on the mounting face  26   a  of a single printed circuit board  26 . There is no particular restriction on the number of LEDs  27  mounted, which may therefore be changed to suit the purpose. 
         [0057]    The printed circuit board  26  comprises, for example, an FPC (flexible printed circuit board) formed in the shape of a strip, and is held with its mounting face  26   a  facing the side edge face  23   c  (light entrance face) of the light guide plate  23 . Accordingly, the LEDs  27  mounted on the mounting face  26   a  of the printed circuit board  26  too face the side edge face  23   c  (light entrance face) of the light guide plate  23 . Thus, when the LEDs  27  emit light, the light strikes the side edge face  23   c  (light entrance face) of the light guide plate  23  and is therethrough introduced into the light guide plate  23 . 
         [0058]    The LEDs  27  are white LEDs, for example those in which a phosphor (fluorescent or phosphorescent substance) that converts blue (blue-violet) LED light into yellow light is combined with a blue LED (blue-violet LED). The LEDs  27  may instead be those in which a phosphor that converts blue (blue-violet) LED light into green and red light is combined with a blue LED (blue-violet LED), or those in which three types of LEDs, namely blue, green, and red LEDs, are combined together. 
         [0059]    For the light from the light source module  25  to efficiently strike the side edge face  23   c  (light entrance face) of the light guide plate  23 , the light guide plate  23  needs to be positioned accurately within the accommodation space of the back chassis  21 . 
         [0060]    Accordingly, in this embodiment, as shown in  FIG. 3 , pressing members  31  which are separate members from the back chassis  21  are, along with the light guide plate  23 , accommodated within the accommodation space of the back chassis  21 , and by use of the pressing members  31 , the light guide plate  23  is positioned accurately within the accommodation space of the back chassis  21 . For the sake of simple illustration, the pressing members  31  are not shown in  FIG. 1 . 
         [0061]    Eight of the pressing members  31  are used, and these pressing members  31  are arranged two-by-two at each of the four side edge faces  23   c  to  23   f  of the light guide plate  23 . 
         [0062]    Specifically, the pressing members  31  are arranged as follows. The two pressing members  31  located at the side edge face  23   c  (light entrance face) of the light guide plate  23  are arranged to face one and the other end portions, respectively, of the side edge face  23   c  (light entrance face) of the light guide plate  23  in the X direction so as not to intercept the light traveling from the light source module  25  to the side edge face (light entrance face)  23   c  of the light guide plate  23  (so as to avoid the region where the light source module  25  is arranged). Likewise, the two pressing members  31  located at the side edge face  23   d  of the light guide plate  23  are arranged to face one and the other end portions, respectively, of the side edge face  23   d  of the light guide plate  23  in the X direction. 
         [0063]    On the other hand, the two pressing members  31  located at the side edge face  23   e  of the light guide plate  23  are arranged to face one and the other end portions, respectively, of the side edge face  23   e  of the light guide plate  23  in the Y direction. Likewise, the two pressing members  31  located at the side edge face  23   f  of the light guide plate  23  are arranged to face one and the other end portions, respectively, of the side edge face  23   f  of the light guide plate  23  in the Y direction. 
         [0064]    These pressing members  31  press the four side edge faces  23   c  to  23   f  of the light guide plate  23  respectively. In other words, in this embodiment, a light guide plate  23  having four side edge faces  23   c  to  23   f  is used, and all of the four side edge faces  23   c  to  23   f  of this light guide plate  23  are pressed by the pressing members  31 . 
         [0065]    Specifically, the side edge face  23   c  of the light guide plate  23  is pressed by the pressing members  31  in one direction along the Y direction (in the direction from the side edge face  23   c  to the side edge face  23   d ), and the side edge face  23   d  of the light guide plate  23  is pressed by the pressing members  31  in the direction opposite from the one direction along the Y direction (in the direction from the side edge face  23   d  to the side edge face  23   c ). On the other hand, the side edge face  23   e  of the light guide plate  23  is pressed by the pressing members  31  in one direction along the X direction (in the direction from the side edge face  23   e  to the side edge face  23   f ), and the side edge face  23   f  of the light guide plate  23  is pressed by the pressing members  31  in the direction opposite from the one direction along the X direction (in the direction from the side edge face  23   f  to the side edge face  23   e ), 
         [0066]    Thus, the side edge faces  23   c  and  23   d  of the light guide plate  23  are in a state pressed in opposite directions by the pressing members  31 , and in addition the side edge faces  23   e  and  23   f  of the light guide plate  23  are in a state pressed in opposite directions by the pressing members  31 , and in this way the light guide plate  23  is held so as not to move in either the X or Y direction. That is, the light guide plate  23  is positioned in the X and Y directions. As seen in a plan view from the direction facing the front face  23   a  of the light guide plate  23 , four corner portions (parts indicated by broken lines in  FIG. 3 ) C of the light guide plate  23  are in a state pressed by the pressing members  32 . 
         [0067]    Specifically, the pressing members  31  are structured as members formed of an elastically deformable cushion material. The cushion material of which the pressing members  31  are formed is, for example, urethane or sponge. 
         [0068]    Moreover, as shown in  FIGS. 3 to 5 , the pressing members  31  are secured to fixing members  32  respectively. The fixing members  32  are resin blocks substantially in the shape of a rectangular parallelepiped, and are formed of polycarbonate resin, polystyrene resin, ABS (acrylonitrile-butadiene-styrene) resin, or the like. The pressing members  31  are secured to the fixing members  32 , and the fixing members  32  are fitted to the bottom portion of the back chassis  21 , so that the pressing members  31  are fixed within the accommodation space of the back chassis  21 . 
         [0069]    The positions at which the pressing members  31  are secured to the fixing members  32  are such that the pressing members  31  are held between the fixing members  32  and the side edge faces  23   c  ( 23   d  to  23   f ) of the light guide plate  23 . When the pressing members  31  are pressing the side edge faces  23   c  ( 23   d  to  23   f ) of the light guide plate  23 , the pressing members  31  are elastically deformed (compression-deformed). That is, the pressing members  31  exert a biasing force that presses the side edge faces  23   c  ( 23   d  to  23   f ) of the light guide plate  23 . 
         [0070]    There is no restriction on how the fixing members  32  are fitted to the bottom portion of the back chassis  21 . For example, though not shown, the fixing members  32  may be fastened to the bottom portion of the back chassis  21  with screws. Or engagement portions may be formed integrally with the fixing members  32  so that the engagement portions of the fixing members  32  are engaged with the bottom portion of the back chassis  21 . 
         [0071]    In this embodiment, as described above, owing to at least one pressing member  31  being arranged at each of the four side edge faces  23   c  to  23   f  of the light guide plate  23  and thus the four side edge faces  23   c  to  23   f  of the light guide plate  23  being pressed individually by their respective pressing members  31 , the light guide plate  23  is held so as not to move (be displaced) in directions (X and Y directions) perpendicular to the thickness direction of the light guide plate  23 ; that is, the light guide plate  23  is positioned in the X and Y directions. This eliminates the need to separately provide positioning members for positioning the light guide plate  23  in the X and Y directions, and thus naturally eliminates the need to form in the light guide plate  23  positioning recesses into which to fit those positioning members. The elimination of the need to form positioning recesses in the light guide plate  23  shortens the processing time of the light guide plate  23  accordingly, and this helps increase the efficiency of the processing of the light guide plate  23 . 
         [0072]    In this embodiment, as described above, owing to the use of an elastically deformable cushion material as the material of the pressing members  31 , even when the light guide plate  23  is expansion-deformed under the influence of heat, the expansion-deformation of the light guide plate  23  can be absorbed by the pressing members  31 , and thus there is no need to previously reserve gaps between the four side edge faces  23   c  to  23   f  of the light guide plate  23  and the pressing members  31  respectively. Moreover, when the four side edge faces  23   c  to  23   f  of the light guide plate  23  are pressed by their respective pressing members  31 , the pressing members  31  are in an elastically deformed (compression-deformed) state; thus even if the light guide plate  23  is contraction-deformed, the pressing members  31  undeform so as not to produce gaps between the four side edge faces  23   c  to  23   f  of the light guide plate  23  and the pressing members  31  respectively. In this way, wobbling of the light guide plate  23  is suppressed. That is, incomplete positioning of the light guide plate  23  is prevented, and the efficiency of the processing of the light guide plate  23  is improved. 
         [0073]    In this embodiment, as described above, owing to the pressing members  31  being arranged two-by-two at each of the four side edge faces  23   c  to  23   f  of the light guide plate  23 , the light guide plate  23  can be held and positioned reliably. Moreover, in this embodiment, owing to the four corner portions C of the light guide plate  23  being in a state pressed by the pressing members  31 , the light guide plate  23  is held and positioned in a well-balanced fashion. 
         [0074]    In this embodiment, as described above, by securing the pressing members  31  to the fixing members  32 , and then fitting the fixing members  32  to the bottom portion of the back chassis  21 , the pressing members  31  can be fixed easily. Moreover, in a case where the pressing members  31  need to be replaced for some reason, by removing the fixing members  32  from the bottom portion of the back chassis  21 , the pressing members  31  can be replaced easily. 
         [0075]    It should be understood that the embodiment presented herein is in every aspect illustrative and not restrictive. The scope of the present invention is defined not by the description of the embodiment given above but by the appended claims, and encompasses any modifications and variations made within the scope and spirit equivalent to those of the claims. 
         [0076]    For example, although the embodiment presented above deals with a case where the pressing members  31  are secured to the fixing members  32  and the fixing members  32  are fitted to the bottom portion of the back chassis  21 , this is not meant to limit the invention; instead, as shown in  FIG. 6 , fixing members  32  having pressing members  31  secured to them may be fitted to a side portion of the back chassis  21 . In that case, the fitting of the fixing members  32  to the side portion of the back chassis  21  can be achieved by a method similar to that used in the case where the fixing members  32  are fitted to the bottom portion of the back chassis  21 . 
         [0077]    As shown in  FIG. 7 , the fixing member  32  may be omitted, and the pressing members  31  may be secured to a side portion of the back chassis  21 . That is, a side portion of the back chassis  21  may be made to function as fixing members  32 . This eliminates the need to reserve space for fitting the fixing members  32  within the accommodation space of the back chassis  21 . This helps reduce the exterior size of the back chassis  21 , and thus helps make the backlight unit  20  compact. The securing of the pressing members  31  to the side portion of the back chassis  21  can be achieved by use of adhesive members  33  of any appropriate kind. 
         [0078]    As shown in  FIG. 8 , the pressing members  31  may be secured to the four side edge faces  23   c  to  23   f  of the light guide plate  23  respectively. In that case, by keeping the non-secured faces of the pressing members  31  opposite from their secured faces in contact with a side portion of the back chassis  21 , it is possible to obtain the same effect as with the embodiment presented above. 
         [0079]    Although the embodiment presented above deals with a case where the pressing members  31  are arranged two-by-two at each of the four side edge faces  23   c  to  23   f  of the light guide plate  23 , this is not meant to limit the invention; instead, the pressing members  31  may be arranged one-by-one, or three-by-three or more, at each of the four side edge faces  23   c  to  23   f  of the light guide plate  23 . Even varying numbers of pressing members  31  may be arranged at each of the four side edge faces  23   c  to  23   f  of the light guide plate  23 . 
         [0080]    For example, as shown in  FIG. 9 , the pressing members  31  may be distributed around the four side edge faces  23   c  to  23   f  of the light guide plate  23  such that two pressing members  31  are arranged at the side edge face  23   c  (light entrance face), that one pressing member  31  elongate in the X direction is arranged at the side edge face  23   d,  and that pressing members  31  elongate in the Y direction are arranged one at each of the side edge faces  23   e  and  23   f.    
         [0081]    Although the embodiment presented above deals with a case where LEDs  27  are used as a light source of the backlight unit  20 , this is not meant to limit the invention; instead, a cold-cathode tube or the like may be used as a light source of the backlight unit  20 . 
         [0082]    Although the embodiment presented above deals with a case where the present invention is applied to a liquid crystal display device, this is not meant to limit the invention; the present invention may be applied to any display devices other than liquid crystal display devices. 
       LIST OF REFERENCE SIGNS 
       [0083]      10  liquid crystal display panel (display panel) 
         [0084]      20  backlight unit (illumination device) 
         [0085]      21  back chassis (casing) 
         [0086]      23  light guide plate 
         [0087]      23   a  front face 
         [0088]      23   b  rear face 
         [0089]      23   c,    23   d,    23   e,    23   f  side edge face 
         [0090]      31  pressing member 
         [0091]      32  fixing member 
         [0092]    c corner portion