Abstract:
Disclosed herein is a rear projection display apparatus including, a screen, a projection mirror; a video apparatus for projecting a picture, an optical unit including a projection lens, a light source, a drive and control circuit, and a structure body for holding the screen, wherein the projection mirror is adjustably provided on the structure body fitted with the screen or on a structure body holding the screen.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]     The present invention contains subject matter related to Japanese Patent Application JP 2005-380626 filed in the Japanese Patent Office on Dec. 29, 2005, the entire contents of which being incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a rear projection display apparatus such that a video apparatus, an optical unit including a projection lens, a light source, a mirror and the like are provided therein and a screen is attached to the front side thereof.  
         [0004]     2. Description of the Related Art  
         [0005]      FIG. 24  shows an example of the internal configuration of a rear projection display apparatus in the related art. This rear projection display apparatus is so configured that an image from a projected image forming part in a projector main body  100  disposed at a rear lower position inside a casing is projected by a projection lens while being projected back or forth by a first plane mirror  101  provided at a front lower position inside the casing and a second plane mirror  105  provided on the rear side in the casing, and is focused from the rear side onto a transmitting screen  103  provided at the front side of the casing, to display an image.  
         [0006]     In such a kind of rear projection display apparatus, the area of the screen can be enlarged while suppressing the front-rear dimension to be small, and, therefore, the overall size of the display can be enlarged more easily than the CRT-type television sets. In view of this, the rear projection display apparatuss have come to be used frequently as a video apparatus in a “home theater” use. Incidentally, Japanese Patent Laid-open No. Hei 11-84533 ( FIG. 1 ) (hereinafter referred to as Patent Document 1) discloses a rear projection display apparatus in which, unlike the configuration of  FIG. 24 , the first plane mirror is not provided, and an image is projected through a projection lens onto the second plane mirror.  
         [0007]     In such a rear projection display apparatus, the image from the projector main body  100  is reflected by the first plane mirror  101  and the second plane mirror  105 , to be focused on the transmitting screen  103 . Therefore, it is important that the plane mirrors are located at predetermined positions at all times. In connection with this, the rear projection display apparatus disclosed in Japanese Patent Laid-open No. Hei 11-142972 (page  2 ,  FIGS. 1 and 2 )(hereinafter referred to as Patent Document 2) has hitherto been known.  
         [0008]     In Patent document 2, description is made of a structure relating to a mirror mounting mechanism of an apparatus for projecting an image onto a screen by a reflecting mirror, such as a rear projector.  
         [0009]     The mirror mounting mechanism has, used in a rear protector in which a reflecting mirror is provided on the back side of an apparatus and an image is projected on a screen through the reflecting mirror, supports and fixes the reflecting mirror at the four sides of the reflecting mirror, whereby warping of the reflecting mirror due to its own weight is restrained as much as possible, so as to maintain the flatness of the reflecting mirror.  
         [0010]     Besides, with the warping of the reflecting mirror thus restrained, distortion of the image on the screen is precluded.  
       SUMMARY OF THE INVENTION  
       [0011]     In the rear projection display apparatus shown in  FIG. 24 , the large second plane mirror is fixed on the rear side inside the casing, and no adjusting mechanism therefor is provided. Therefore, where a defective product is generated due to dispersion of mounting, it is impossible to easily correct the defect and to enhance the positional accuracy as to the mirror position, in this related art. As a countermeasure against this problem, it has been the common practice to support and fix the reflecting mirror on the rear side in the casing through the four sides of the reflecting mirror, to restrain the warping of the reflecting mirror, as described in Patent document 2.  
         [0012]     On the other hand, in a rear projection display apparatus, for a more reduction in the installation area, a further reduction in the front-rear dimension (depth size) of the display has been investigated, for example, by adopting a structure in which the plane mirror  105  in  FIG. 24  provided in related art on the rear side is disposed on the ceiling plate side and the image is nearly vertically projected from the projector.  
         [0013]     In such a configuration in which the plane mirror is disposed on the side of the ceiling plate of the rear projection display apparatus, the condition for the relative positional relationship between the plane mirror and the screen becomes severer than in the related art. Therefore, it is essential that the position of the plane mirror can be adjusted.  
         [0014]     Thus, there is a need to provide a rear projection display apparatus in which a plane mirror for projection is disposed on the ceiling plate side and which includes a mirror adjusting mechanism having sufficient rigidity and positioning accuracy.  
         [0015]     According to an embodiment of the present invention, there is provided a rear projection display apparatus including, a screen, a projection mirror, a video apparatus for projecting a picture, an optical unit including a projection lens, a light source, a drive and control circuit, and a structure body for holding the screen, wherein the projection mirror is adjustably provided on the structure body fitted with the screen or on a structure body holding the screen.  
         [0016]     According to the rear projection display apparatus in the present invention configured as just-mentioned, the projection mirror is adjustably provided on the structure body so configured as to have an increased rigidity. This makes it possible to more easily carry out the final adjustment at the stage upon assembly of the structure body (outer box) or in the site of installation of the display by the user, as compared with the configuration in the past in which the warping of the reflection mirror due to its own weight is restrained as much as possible, and to maintain flatness of the mirror, by supporting and fixing the mirror through the four sides of the mirror.  
         [0017]     According to the rear projection display apparatus in the present invention, the installation area can be reduced, and the projection mirror can be held without loosing the flatness thereof. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a perspective view, from the front side, of a rear projection display apparatus according to one embodiment of the present invention;  
         [0019]      FIG. 2  is a perspective view, from the rear side, of the rear projection display apparatus shown in  FIG. 1 ;  
         [0020]      FIG. 3  is an exploded perspective view, from the front side, of the rear projection display apparatus shown in  FIG. 1 ;  
         [0021]      FIG. 4  is a perspective view, from the front side, of the display unit shown in  FIG. 3 ;  
         [0022]      FIG. 5  is a perspective view, from the rear side, of the display unit shown in  FIG. 3 ;  
         [0023]      FIG. 6  is a perspective view, from the rear side, of only the frame structure body in the display unit shown in  FIG. 5 ;  
         [0024]      FIGS. 7A and 7B  are perspective views of the projection mirror shown in  FIG. 5 , in which  FIG. 7A  is a perspective view from the upper side of the projection mirror, and  FIG. 7B  is a perspective view from the upper side of the projection mirror in the inverted state;  
         [0025]      FIG. 8  is a sectional view at the center of the projection window shown in  FIG. 5 , around the optical unit;  
         [0026]      FIG. 9  illustrates an example of optical path of a picture projected in the rear projection display apparatus according to the one embodiment of the present invention;  
         [0027]      FIG. 10  is a partly broken perspective view of four frames constituting a screen frame in the frame structure body shown in  FIG. 6 ;  
         [0028]      FIGS. 11A  to  11 D are sectional views of the four frames shown in  FIG. 10 , in which  FIG. 11A  shows the top frame,  FIG. 11B  shows the right side frame,  FIG. 11C  shows the left side frame, and  FIG. 11D  shows the bottom frame;  
         [0029]      FIG. 12  is a perspective view showing the condition where the bottom frame and the left side frame, in the frame structure body shown in  FIG. 6 , are positioned and fixed;  
         [0030]      FIG. 13  is a perspective view showing the condition where the top frame and the left side frame, in the frame structure body shown in  FIG. 6 , are positioned and fixed;  
         [0031]      FIG. 14  is a perspective view showing the condition where the left frame support for connecting the bottom frame and the left side frame, in the frame structure body shown in  FIG. 6 , in a bracing manner is fixed to the left side frame;  
         [0032]      FIG. 15  is a sectional view for illustrating a mounted state of the screen shown in  FIG. 4 ;  
         [0033]      FIG. 16  is an exploded perspective view of the mirror fixing plate shown in  FIG. 6 ;  
         [0034]      FIG. 17  is a perspective view of a mirror holding plate shown in  FIG. 7A ;  
         [0035]      FIG. 18  is a sectional view for illustrating the condition, immediately before mounting onto the top frame, of the projection mirror in the display unit according to one embodiment of the present invention;  
         [0036]      FIG. 19  is a sectional view showing the mounted condition of the projection mirror in the display unit according to one embodiment of the present invention;  
         [0037]      FIG. 20  is a sectional view taken at the center of the projection mirror shown in  FIG. 7A ;  
         [0038]      FIGS. 21A  to  21 D are perspective views of members used for the projection mirror shown in  FIGS. 7A and 7B , in which  FIG. 21A  is a view from above of a support piece,  FIG. 21B  is a view from above of the support piece in the inverted state,  FIG. 21C  is a view of a presser piece, and  FIG. 21D  is a view of a shaft piece;  
         [0039]      FIG. 22  is an enlarged perspective view of an essential part, showing the condition immediately after the mounting of the projection mirror shown in  FIG. 18  to the top frame;  
         [0040]      FIG. 23  is a partly sectional perspective view, showing an essential part in section, of the projection mirror shown in  FIG. 19  in its mounted state; and  
         [0041]      FIG. 24  illustrates the optical path in projection of a picture onto a screen in a rear projection display apparatus according to the related art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0042]     Now, an embodiment of the present invention will be described below referring to FIGS.  1  to  23 .  
         [0043]      FIG. 1  is a perspective view, from the front side, of a rear projection display apparatus according to the present embodiment, and  FIG. 2  is a perspective view, from the rear side, of the rear projection display apparatus. Besides,  FIG. 3  is an exploded perspective view showing a general configuration of the rear projection display apparatus.  
         [0044]     In this embodiment, the video display screen of the rear projection display apparatus is, for example, of the 50-inch type, and the front-rear dimension (thickness) of the display is as small as 30 cm, for example.  
         [0045]     Numeral  1  in FIGS.  1  to  3  denotes the rear projection display apparatus. As shown in  FIG. 3 , the rear projection display apparatus  1  has a configuration in which, to a display unit  2  provided with a screen  3  of the rear projection type at its front side, an outer frame  4  and a cover frame  6  are mounted from the front side, and a rear cover  5  is mounted from the rear side. Here, the outer frame  4 , the cover frame  6  and the rear cover  5  constitute a structure body (outer box) of the rear projection display apparatus  1 .  
         [0046]     The screen  3  has a structure in which a front-side transparent glass plate with its front surface matt treated and with a lenticular lens sheet adhered to its rear surface and a rear-side transparent glass plate with a Fresnel lens sheet adhered to its rear side are so disposed as to keep a predetermined gap therebetween.  
         [0047]     As shown in  FIG. 1 , the cover frame  6  having a rectangular frame-like shape is disposed in the periphery of the screen  3  on the front side, the outer frame  4  having a horizontally elongate rectangular frame-like shape is disposed in the periphery of the cover frame  6 , and the rear cover  2  is provided on the rear side so as to cover the display unit  2  (see  FIG. 2 ). Incidentally, numeral  7  in  FIG. 1  denotes a base part cover provided on the front lower side of the display unit  2 .  
         [0048]     In addition, as shown in  FIG. 2 , the rear cover  5  provided on the rear side of the rear projection display apparatus  1  has a configuration in which a mirror adjusting part lid  5   a  is provided at an upper portion, a cover  5   b  is provided for a box-like recessed part for containing an electric circuit unit which is not shown, and a cooling fan cover  5   c  is provided at a position corresponding to a cooling fan unit  57  for cooling a lamp (not shown) provided in a lamp house  58  in the display unit  2  (see  FIG. 5 ). Here, the mirror adjusting part lid  5   a  is destined to be opened to expose a mirror holding plate  34  (described later) in adjusting a projection mirror  30  (described later).  
         [0049]     Furthermore, as shown in  FIG. 2 , speaker units  8 ,  8  each provided integrally with a decorative panel on the front side thereof are provided in vertically elongate regions formed between left and right portions of the outer frame  4  and left and right portions of the rear cover  5 .  
         [0050]     Now, the display unit  2  shown in  FIG. 3  will be described below referring to FIGS.  4  to  9 .  
         [0051]      FIG. 4  is a perspective view, from the front side, of the display unit  2 ;  FIG. 5  is a perspective view, from the rear side, of the display unit  2 ; and  FIG. 6  is a perspective view, from the rear side, of a frame structure body of the display unit  2 .  
         [0052]     As shown in  FIG. 4 , the display unit  2  has the screen  3  inside a substantially rectangular frame composed of a laterally long bottom frame  11  disposed on the bottom side, left and right side frames  12  and  13  disposed upright on the left and right of the bottom frame  11 , and a top frame  14  provided on the upper end side of the side frames  12 ,  13 . The outer periphery of the screen  3  are retained by screen retainers  9   a ,  9   b ,  9   c  and  9   d  so that the screen  3  would not come out of position. Incidentally, mirror bearings  2   a  and  2   b  in  FIG. 4  are for engagement with a shaft  38   a  of a shaft piece  38  provided for the projection mirror  30  which will be described later.  
         [0053]     Besides, as shown in  FIG. 5 , the display unit  2  includes the lamp house  58  and the cooling fan unit  57  on the rear side of the bottom frame  11 ; additionally, there is provided an optical unit  50  which separates the light from the lamp into the three primary colors of light, namely, R (red), G (green) and B (blue), forms three color pictures through three liquid crystal panels (not shown), and projects the pictures via a projection window  51 . As the three liquid crystal panels, in this embodiment, reflection-type liquid crystal image display panels are used. Incidentally, numeral  55  in  FIG. 5  denotes a projection control circuit board for controlling the pictures on the three liquid crystal panels incorporated in the optical unit  50 .  
         [0054]     In addition, as shown in  FIG. 5 , the display unit  2  has a configuration on the rear side in which a left frame support  16  is provided between the left side frame  12  and the bottom frame  11 , a right frame support  15  is provided between the right side frame  13  and the bottom frame  11 , and a light shielding plate  18  for avoiding the influence of the light leaking from the optical unit  50  on the screen  3  and functioning also as reinforcement is provided between the left and right side frames  12 ,  13  and the bottom frame  11 .  
         [0055]     Further, as shown in  FIG. 5 , the display unit  2  is provided with a mirror support  17  composed of a bent sheet metal, at upper end portions of the left and right side frames  12  and  13 . The mirror support  17  is so shaped, as viewed from the upper side thereof, as to form a trapezoidal frame together with the top frame  14 . A mirror fixing plate  19  is bridgingly provided substantially at a central position between the top frame  14  and the mirror support  17  ( FIG. 6 ). Incidentally, a mirror holding plate  34  (described later) is engaged with the mirror fixing plate  19 , whereby the projection mirror  30  shown in  FIGS. 7A and 7B  is positioned and fixed.  
         [0056]     The principle of projection onto the screen  3  by the display unit  2  configured as just-mentioned will be described.  
         [0057]      FIG. 8  is a sectional view taken at the center of the projection window  51  shown in  FIG. 5 , around the optical unit  50 . The R, G and B light pictures formed by the three liquid crystal panels as above-mentioned are synthesized into a picture, which is projected from the viewer&#39;s side of the surface of sheet of  FIG. 8  toward a plane mirror  52  on the depth side (opposite side), and the optical path is bent by about 90° by the plane mirror  52 , so that the picture-carrying light is incident on a convex mirror  53 . As shown in  FIG. 9  showing the entire part of the optical path, the picture-carrying light reflected by the convex mirror  53  is reflected further by a non-spherical mirror  54 , to be transmitted through the projection window  51 , and is then reflected by a plane mirror  31  of the projection mirror  30 , to be projected on the screen  3  on the front side.  
         [0058]     In the display unit  2  according to this embodiment, as shown in  FIG. 9 , the ratio of the height of the display unit  3  to the front-rear distance (depth) from the screen  3  on the front side to the plane mirror  52  in the optical unit  50  is about 10:3, indicating that the height is large as compared with the front-rear direction (depth). In other words, the angle formed between the direction of projection onto the plane mirror  52  and the horizontal direction is extremely larger, as compared with that in a rear projection display apparatus according to the related art.  
         [0059]     Therefore, even a slight deformation of the frame structure body shown in  FIG. 6  would cause distortion or fuzziness in the picture projected on the screen  3 . Accordingly, it is essential to the display unit  2  in this embodiment that a frame structure body less liable to change (deteriorate) with age and capable of maintaining a high positional accuracy be adopted and that fine adjustment of the angle of the projection mirror  30  can be easily carried out, for example, after movement such as transportation.  
         [0060]     Now, the frame structure of the display unit  2  in this embodiment and a structure for mounting and adjusting the mirror will be sequentially described below.  
         [0061]     First, the frame structure body in the display unit  2  according to this embodiment will be described referring to  FIGS. 1, 4 ,  6 , and  10  to  16 .  
         [0062]      FIG. 10  is a perspective view, partly omitted, of the bottom frame  11 , the left and right side frames  12 ,  13  and the top frame  14 , of the frame structure body shown in  FIG. 6 .  FIGS. 11A  to  11 D are sectional views of the four frames, in which  FIG. 11A  shows the top frame  14 ,  FIG. 11B  shows the right side frame  13 ,  FIG. 11C  shows the left side frame  12 , and  FIG. 11D  shows the bottom frame  11 .  
         [0063]     These frames  11 ,  12 ,  13 ,  14  are formed in rod-like or plate-like shape by extrusion of an alloy of aluminum or the like through such dies that they assume uniform sectional shapes as shown in  FIG. 10  and  FIGS. 11A  to  11 D. Here, the left and right side frames  12  and  13  are members extruded by use of the same die.  
         [0064]     As shown in  FIG. 11D , the bottom frame  11  has a structure in which four space regions A to D substantially rectangular in sectional shape are provided by use of partition walls in a bottom line portion of a roughly L-shaped form, and a single space region E substantially rectangular in sectional shape is provided in a rising portion of the roughly L-shaped form. In addition, screw passing grooves  11   a ,  11   b ,  11   c , lid each having a roughly cylindrical inside surface for a fixing screw  10   a  (described later) are provided integrally in the bottom frame  11 , at four positions shown in  FIG. 11D . Besides, the face  11 - 1  on the upper side of the space region E shown in  FIG. 11D  of the bottom frame  11  is provide with a plate-like projection  11   e  along the direction perpendicular to the surface of sheet of  FIG. 11D , and the screen  3  is mounted on the face  11 - 1  and the surface  11 - 2  of the plate-like projection  11   e.    
         [0065]     In addition, the partition walls in the section of the bottom frame  11  are provided with thick wall parts  11   h  and  11   i , and a plate-like part  11   f  is extendingly provided on the left side in  FIG. 11D  of the bottom frame  11 . Incidentally, spring pins  10   b  (described later) for positioning the side frames  12 ,  13  are erectingly provided at the thick wall part  11   h ,  11   i , and the plate-like part  11   f  constitutes a base part, which is covered with the base part cover  7  shown in  FIG. 1 .  
         [0066]     As shown in  FIG. 11B , the left side frame  12  has a structure in which two space regions F and G are formed by use of a partition wall at a substantially central position of a tube roughly rectangular in section, a groove  12   a  recessed to the side of the region F is formed, and a groove  12   b  having a roughly cylindrical inside surface is formed at an outside wall of the region G. Besides, as shown in  FIG. 10 , the left side frame  12  is provided in its upper portion with screw passing holes for two fixing screws  10   a  and with passing holes for two spring pins  10   b , and is provided in its lower portion with screw passing holes  10   a  for three fixing screws  10   a  and with passing holes for two spring pins  10   b.    
         [0067]     Here, the screw passing holes provided in the upper portion of the left side frame  12  for passing the two fixing screws  10   a  therethrough are provided at positions corresponding to screw passing grooves  14   b  and  14   c  in the top frame  14  to be described later, and the passing holes for the two springs pins  10   b  are provided at positions corresponding to thick wall parts  14   d  and  14   e  of the top frame  14  to be described later (see  FIG. 11A ).  
         [0068]     In addition, the three screw passing holes provided in the lower portion of the left side frame  12  are provided at positions corresponding to the screw passing grooves  11   b ,  11   c  and  11   d  in the bottom frame  11 , and the passing holes for the two spring pins  10   b  are provided at positions corresponding to the thick wall parts  11   h  and  11   i  of the bottom frame  11  (see  FIG. 11D ).  
         [0069]     Similarly, as shown in  FIG. 11C , the right side frame  13  has a structure in which two space regions F′ and G′ are formed by use of a partition wall at a substantially central position of a tube roughly rectangular in section, a groove  13   a  recessed to the side of the region F′ is formed, and a groove  13   b  is formed on the outside of the region G′. Besides, a total of five screw passing holes and a total of four spring pin passing holes are provided at predetermined positions.  
         [0070]     Incidentally, the grooves  12   a  and  13   a  in the left and right side frames  12  and  13  are used for fitting therein bent portions provided in longitudinal sides of the left and right screen retainers  9   b  and  9   c  shown in  FIG. 4  above, while the grooves  12   b  and  13   b  are used for fitting therein a seal member formed of a flexible foam of foamable resin (see  FIG. 15 ).  
         [0071]     As shown in  FIGS. 10 and 11 A, the top frame  14  is formed to be roughly inverse L-shaped in section, and a portion kept substantially horizontal is integrally provided at its two positions with screw passing grooves  14   b  and  14   c  having a roughly cylindrical inside surface for passing the fixing screws  10   a  therein. In addition, on the lower side of a drooping face  14 - 1  on the left side in  FIG. 11A  of the top frame  14 , a face  14 - 2  is formed orthogonally to the drooping face  14 - 1 . Further, a projection  14   f  roughly inverse triangular in section and having a face  14 - 3  orthogonal to the face  14 - 2  is formed along the direction perpendicular to the surface, and the screen  3  is disposed so as to abut on the face  14 - 3  of the projection  14   f.    
         [0072]     In addition, the top frame  14  is provided with thick wall parts  14   d  and  14   e , and a recessed groove  14   a  having a cylindrical surface is formed on the upper side of the projection  14   f  shown in  FIG. 11A  of the top frame  14 . Incidentally, the cylindrical-surfaced recessed groove  14   a  serves as a sliding surface for turning of the projection mirror  30 , and the spring pins  10   b  for positioning the side frames  12  and  13  are erectingly provided on the thick wall parts  14   d  and  14   e.    
         [0073]     In assembling the frames  11 ,  12 ,  13  and  14  configured as above, first, the fixing screws  10   a  are screw-engaged into the screw passing grooves  11   b ,  11   c  and lid provided at the end side face portion of the bottom frame  11  shown in  FIG. 10  through the three each screw passing holes provided in the lower portions of the left and right side frames  12  and  13 , to tentatively fix the bottom frame  11  and the left and right side frames  12  and  13  to each other (see  FIG. 12 ). Then, the fixing screws  10   a  are screw-engaged into the screw passing grooves  14   b  and  14   c  provided at the end side face portion of the top frame  14  through the two each screw passing holes provided in the upper portions of the left and right side frames  12  and  13 , to tentatively fix the top frame  14  to the left and right side frames  12  and  13  (see  FIG. 13 ).  
         [0074]     Thereafter, as shown in  FIG. 6 , the right frame support  15  is tentatively fixed in a bracing manner between the bottom frame  11  and the right side frame  13  by the fixing screws  10   a , and the left frame support  16  is tentatively fixed in a bracing manner between the bottom frame  11  and the left side frame  12  by the fixing screws  10   a  (see  FIG. 14 ).  
         [0075]     Here, the right frame support  15  and the left frame support  16  are provided in the bracing manner relative to the bottom frame  11  so as to form an angle of, for example, about 45° to the top frame  14 , as viewed from the upper side of the display unit  2 , so that the rigidity of the assembly against deforming forces in the x-direction and the y-direction in  FIG. 5  after permanent fixing will be enhanced.  
         [0076]     As a result, a roughly rectangular screen frame composed of the frames  11 ,  12 ,  13  and  14  and provided with the screen  3  is formed, and the frame structure body including the left and right frame supports  15  and  16  for supporting the screen frame to prevent the screen frame from falling down is formed.  
         [0077]     Incidentally, the base part plate  25  in  FIG. 12  is a metal plate provided on the lower side of the plate-like part  11   f  of the bottom frame  11 , for mounting thereto the plate part cover  7  shown in  FIG. 1 .  
         [0078]     The screen frame of the frame structure body composed of the frames  11 ,  12 ,  13  and  14  and the left and right frame supports  15  and  16  tentatively fixed is permanent-fixed by the fixing screws  10   a  so that the left and right side frames  12  and  13  are set perpendicular to the face  11 - 3  shown in  FIG. 6  of the bottom frame  11 , and that the face  11 - 2  shown in  FIG. 11D  of the bottom frame  11 , the face  12 - 1  shown in  FIG. 11B  of the left side frame  12 , the face  13 - 1  shown in  FIG. 11C  of the right side frame  13 , and the face  14 - 1  shown in  FIG. 11A  of the top frame  14  are set flat with each other, the settings being made, for example, by use of assembly jigs (not shown) or the like.  
         [0079]     In order that the permanent-fixed condition can be maintained even upon stacking of the fixing screws  10   a , larger passing holes than the original are bored in the thick wall parts  11   h  and  11   i  of the bottom frame  11  and the thick wall parts  14   d  and  14   e  of the top frame  14  from the side of the passing holes for the four spring pins  10   b  provided respectively on the upper and lower sides of the left and right side frames  12  and  13  by a drill or the like.  
         [0080]     Besides, the bottom frame  11  and the top frame  14  are slacklessly positioned relative to the left and right side frames  12  and  13  by the spring pins  10   b  erectingly provided in the holes in the thick wall parts  11   h ,  11   i ,  14   d  and  14   e . Here, in boring the holes in which to erectingly provide the spring pins  10   b , a drill with a diameter larger than the diameter of the spring pin passing holes is used so that the diameter of the passing holes for the spring pins  10   b  after the boring will be equal to the diameter of the holes in the thick wall parts  11   h ,  11   i ,  14   d  and  14   e  and that no chattering will be generated between the spring pins  10   b  erectingly provided in these holes and the left and right side frames  12  and  13 .  
         [0081]     In addition, the left and right frame supports  15  and  16  are fixed and reinforced by use of rivets  10   c  shown in  FIG. 14  or the like so that deformation thereof can be suppressed to a slight level even when a great force is exerted on the whole frame. Here, the reason why the reinforcement of the left and right frame supports  15  and  16  is not conducted by use of screws lies in that a sufficient fastening strength by screws cannot be obtained against a large deforming force, since the fixing of the left and right frame supports  15  and  16  is conducted relative to the comparatively thin side wall faces of the left and right side frames  12  and  13  and the bottom frame  11  which are extruded members.  
         [0082]     In addition, as shown in  FIGS. 6 and 8 , at a lower portion of the screen frame composed of the frames  11 ,  12 ,  13  and  14 , there is provided a light shielding plate  18  for shielding the light leaking to the screen and serving also as a reinforcement plate for restraining the deformation of the screen frame in the direction of arrow in the figure. Here, for enhancing the rigidity of the light shielding plate  18  formed of a comparatively thin sheet metal, the light shielding plate  18  is provided with a plurality of oblong recessed parts and its upper end lower edges are folded back, as shown in  FIG. 6 .  
         [0083]     Besides, the mirror support  17  is fixed on the upper side of the left and right side frames  12  and  13 , as above-mentioned, and the mirror fixing plate  19  is provided between the mirror support  17  and the top frame  14 .  
         [0084]     In this way, the frame structure body in the display unit  2  in this embodiment is assembled.  
         [0085]     In the frame structure body of the rear projection display apparatus in this embodiment configured as above, the screen frame for fixing the screen  3  is configured by use of the bottom frame  11 , the left and right side frames  12  and  13 , and the top frame  14  which are each formed by extrusion of a metal such as an aluminum alloy to be uniform in sectional shape, to be light in weight and to have high rigidity. In this case, the fixing screws  10   a  and the spring pin  10   b  are passed through the fixing screw passing grooves  11   a  to  11   d  and the thick wall parts  11   h  and  11   i  provided in the sections of the bottom frame  11  and the top frame  14 , whereby the screen frame is assembled with high accuracy and so as to be free of slackening.  
         [0086]     In addition, for restraining deformation of the screen frame, the left and right frame supports  15 ,  16  are bracingly disposed between the bottom frame  11  and the left and right side frames  12 ,  13 , whereby the frame structure body is strengthened.  
         [0087]     Further, the screen  3  having a damper sheet  3   a  on its rim is provided in the state of being retained by the screen retainers  9   a ,  9   b ,  9   c ,  9   d  so as to be positioned by the faces  11 - 1  and  11 - 2  ( FIG. 1D ) of the bottom frame  11  constituting the screen frame and the face  14 - 3  ( FIG. 11A ) of the top frame  14  constituting the screen frame.  
         [0088]     In addition, for maintaining the accuracy of the projection mirror  30 , the mirror support  17  having the mirror fixing plate  19  ( FIG. 6 ) substantially at the center thereof in relation to the left and right side frames  12  and  13  is provided at an upper portion of the screen frame, whereby rigidity is secured. Besides, one end side of the projection mirror  30  is turnably mounted in the cylindrical-surfaced recessed groove  14   a  provided as one body with the top frame  14 , and the other end side of the projection mirror  30  is mounted by the mirror holding plate  34  ( FIG. 7A ) so as to have a predetermined inclination angle.  
         [0089]     Further, the optical unit  50  is positioned by positioning pins (not shown) provided in the positioning holes  11 - 4  (see  FIG. 6 ) of the bottom frame  11 .  
         [0090]     Now, a structure for mounting the projection mirror  30  on the frame side will be described below referring to FIGS.  16  to  18 .  
         [0091]     As shown in  FIG. 16 , which is an exploded perspective view, the mirror fixing plate  19  is produced in a substantially line-symmetric shape by bending a sheet metal of steel or the like. The sheet metal is so bent that the mirror fixing plate is substantially rectangular in shape as viewed from above, the cross section on one end side of the rectangle is angular U-shaped, and the cross section at a central portion of the rectangle is in a generally angular U-shaped form with its end edges bent. In addition, the other end side of the mirror fixing plate  19  is provided with a roughly rectangular opening  19   c , and is bent, as shown in  FIG. 16 .  
         [0092]     Besides, three screw passing holes  19   a  for fixing to the top frame  14  is provided on the one end side of the rectangle, a comparatively large-width slit  19   d , a slot  19   f  and a screw hole  19   g  are provided in a roughly central portion of the rectangle on the center line along the longitudinal direction of the rectangle, two slits  19   e  are provided on both sides of the slit  19   d  on opposite sides of the center line, and six screw holes  19   b  for fixing to the mirror support  17  are provided in a bent part on the other end side of the rectangle.  
         [0093]     Numeral  20  in  FIG. 16  denotes a tentative support produced by bending an elastic sheet metal of a stainless steel or the like. The tentative support  20  is provided with an engaging pawl  20   a , a large round hole  20   b , a small round hole  20   c , and two bent parts  20   d . Here, the two bent parts  20   d  are so sized that they can be inserted into the two slits  19   e  in the mirror fixing plate  19 , and are so located that in the condition where the bent parts  20   d  are inserted, the large round hole  20   b  corresponds to the slot  19   f , and the small round hole  20   c  to the screw hole  19   g . In addition, the large round hole  20   b  is so sized that, even when an adjusting screw  21  (described later) is moved inside the slot  19   f  in the mirror fixing plate  19 , the large round hole  20   b  does not interfere with a flange part  21   a  of the adjusting screw  21 . The small round hole  20   c  is set to be larger than the screw diameter of a fixing screw  23 .  
         [0094]     In addition, numeral  21  in  FIG. 16  denotes the adjusting screw. The adjusting screw  21  has a configuration in which, for example, the circular flange part  21   a  is formed as one body with a head part of a hexagonal-holed bolt. The diameter and the thickness of the flange part  21   a  are set to be smaller than the large round hole  20   b  in the tentative support  20  and to be larger than the thickness of the tentative support  20 , respectively. The adjusting screw  21  has fine threads, with a screw pitch of 0.2 mm, for example.  
         [0095]     Besides, numeral  22  in  FIG. 16  denotes a fixing plate for fixing the tentative support  20 . The fixing plate  22  is provided with large and small round holes  22   a  and  22   b , and is provided at its one end with a bent part  22   c  roughly Z-shaped in longitudinal section. The large and small round holes  22   a  and  22   b  are located at positions corresponding respectively to the large and small round holes  20   b  and  20   c  in the tentative support  20 . The large round hole  22   a  is larger in diameter than the head part of the adjusting screw  21 , and the small round hole  22   b  is larger than the screw diameter of the fixing screw  23 .  
         [0096]     The mirror fixing plate  19  configured as above is bridgingly provided between roughly central portions of the top frame  14  and the mirror support  17 , as above-mentioned ( FIG. 6 ). As shown in  FIG. 18 , of the mirror fixing plate  19 , the side where the three screw passing holes  19   a  are provided is fixed to the top frame  14  by three fixing screws  29  screw-engaged from below, and the side where the opening  19   c  and the six screw holes  19   b  are provided is fixed to the mirror support  17  by six screws  32 .  
         [0097]     As a result, the mirror fixing plate  19  is fixed to both the top frame  14  and the mirror support  17 , and also plays the role of a reinforcement member for restraining deformation of the mirror support  17  produced by bending a sheet metal.  
         [0098]     Meanwhile, the tentative support  20 , the adjusting screw  21 , the fixing plate  22 , and the fixing screw  23  as above-described are used in a predetermined sequence in mounting the projection mirror  30  to the top frame  14  and the mirror support  17 . Here, the condition where the component parts are mounted to the mirror fixing plate  19  will be described briefly.  
         [0099]     As shown in  FIG. 16 , first, the bent parts  20   d ,  20   d  of the tentative support  20  are inserted into the slits  19   e ,  19   e  in the mirror fixing plate  19 , and then the adjusting screw  21  is passed through the slot  19   f . In this instance, the flange part  21   a  of the adjusting screw  21  is arranged in the large round hole  20   b  in the tentative support  20  so as not to interfere with the large round hole  20   b . Next, the fixing plate  22  is so mounted that the bent part  22   c  is caught by the slit  19   d  in the mirror fixing plate  19 , then the fixing screw  23  is passed through the round holes  22   b  and  20   c  and is screw-engaged into the screw hole  19   g  in the mirror fixing plate  19 , whereby the flange part  21   a  of the adjusting screw  21  is pressed by the fixing plate  22  and the adjusting screw  21  is fixed so as not to slacken.  
         [0100]     Now, the projection mirror  30  will be describe below referring to  FIGS. 5, 7A ,  7 B, and  17  to  21 .  
         [0101]     Here,  FIG. 7A  is a perspective view, from the upper side, of the projection mirror  30 ; and  FIG. 7B  is a perspective view, from the upper side, of the projection mirror  30  in its inverted state.  FIG. 17  is a perspective view of a mirror holding plate  34 ,  FIG. 18  is a sectional view showing the condition immediately before the mounting of the projection mirror  30  shown in  FIG. 7A  to the top frame, and  FIG. 19  is a sectional view showing the condition where the projection mirror  30  is mounted to the top frame, taken along the center axis of the projection mirror  30 .  FIG. 20  is a sectional view taken at the center axis of the projection mirror shown in  FIG. 7A .  FIG. 21A  is a perspective view, from the upper side, of a left support piece;  FIG. 21B  is a perspective view, from above, of the left support piece in its inverted state;  FIG. 21C  is a perspective view of a retainer piece; and  FIG. 21D  is a perspective view of a shaft piece.  
         [0102]     As shown in  FIGS. 7A and 7B , the projection mirror  30  includes the plane mirror  31  composed of a glass plate having a reflective surface  31 - 1 , long and short two holding frames  32  and  33 , a mirror holding plate  34 , left and right support pieces  35  and  36 , four retainer pieces  37  and three shaft pieces  38 ,  38  and  39 , belt-like mirror protective sheets  32   a  and  33   a  (see  FIG. 20 ), and the like.  
         [0103]     As shown in  FIGS. 7A and 7B , the plane mirror  31  is a glass plate provided with right-angled triangular cutouts at two corner portions on the side of two shorter sides of one of the opposed longer sides of a rectangular shape, and a reflective film is formed on one surface of the glass plate. Here, the reflective film is formed by vapor depositing a metal such as aluminum on the glass plate.  
         [0104]     As indicated by hatching in  FIG. 20 , the long holding frame  32  is a frame formed by extrusion of an aluminum alloy or the like and being roughly angular U-shaped in section and having a groove, the length thereof is approximately equal to the length of the longer sides of the plane mirror  31 , and the groove width is set larger than the plane mirror  31 . Besides, the long holding frame  32  is provided with screw holes (not shown) at predetermined positions.  
         [0105]     On the other hand, as indicated by hatching in  FIG. 20 , the short holding frame  33  is a frame formed by extrusion of an aluminum alloy or the like, roughly y-shaped in section, and having large and small two grooves  33   a  and  33   b , the length thereof is approximately equal to the length of the cutout-side side opposite to the longer side of the plane mirror  31 , and the groove width of the large groove  33   a  is set larger than the thickness of the plane mirror  31 . Besides, the short holding frame  33  is provided with screw holes (not shown) at predetermined positions. Incidentally, two side walls  33 - 1  and  33 - 2  of the small groove  33   b  are formed as reinforcement ribs for increasing the rigidity of the short holding frame  33  and making the short holding frame  33  less liable to be deformed.  
         [0106]     As shown in  FIG. 7A , the mirror holding plate  34  is for fixing the two holding frames  32  and  33  at their roughly central portions. The mirror holding plate  34  has a complicated shape having a roughly rectangular line-symmetric general shape and having recessed and projected shapes, as shown in  FIG. 17 , and has a thin wall structure as shown in  FIG. 20 ; therefore, the mirror holding plate  34  is produced by die-casting of an aluminum alloy or the like and thereafter finishingly processing predetermined portions of the cast body.  
         [0107]     As shown in  FIG. 17 , the mirror holding plate  34  has a configuration in which, first, two elongate boxes are arranged side by side in parallel, and, in connection with upper edge portions of the two boxes, a portion of which the depth is larger than the longer sides of the boxes and the width is approximately equal to the outermost width at the upper edge portions of the two boxes arranged side by side is formed. Then, a flat plate having a face  34 - 4  is integrally provided on the upper side, and the bottom surfaces of the two boxes are left exposed. In this case, an overhang part  34   p  is provided on the depth side in  FIG. 17  of the face  34 - 4 , and flat surface parts  34   o ,  34   o  are formed on the viewer&#39;s side of the face  34 - 4 .  
         [0108]     Further, in the mirror holding plate  34 , outer peripheral edges of a half on the viewer&#39;s side in  FIG. 17  are extended upward to form side walls, and a slant surface  34 - 4  is formed on the viewer&#39;s side in  FIG. 17  continuous to a region S, between the two boxes, of the face  34 - 4 .  
         [0109]     As shown in  FIG. 17 , on the upper side of the mirror holding plate  34 , there are arranged a roughly cylindrical spring guide  34   d  provided on the center line and on the slant surface  34 - 3 , a screw hole  34   e  provided along the center axis of the cylindrical portion of the spring guide  34   d , a roughly rectangular opening  34   h , and an engageable part  34   f . In addition, as shown in  FIG. 17  on opposite sides of the center line of the line symmetry, the overhang part  34   p  is provided with reinforcement projected parts  34   g  triangular in section, and roughly rectangular wing-like grips  34   c ,  34   c  are provided on the upper side of both side surfaces on opposite sides of the spring guide  34   d.    
         [0110]     Here, as shown in  FIG. 20 , the center axis of the spring guide  34   d  is slightly inclined relative to the plane mirror  31 . In this case, the inclination angle is so set that the center axis is substantially orthogonal to the upper face of the mirror fixing plate  19  in the condition where the projection mirror  30  is mounted in position as shown in  FIG. 19 . Besides, the opening  34   h  is provided with such a width that the engaging pawl  20   a  of the above-mentioned tentative support  20  can be removably inserted therein, and the engageable part  34   f  is provided at such a position as to make contact with the tip end of the engaging pawl  20   a  in the process of putting the engaging pawl  20   a  into the inserted state shown in  FIG. 19 .  
         [0111]     The overhang part  34   p  shown in  FIG. 17  of the mirror holding plate  34  has a lower surface  34 - 2  finished to be a flat surface, and is provided with screw passing holes  34   b ,  34   b . In addition, on the side where the engageable part  34   f  and the flat surface parts  34   o .  34   o  are formed, of the mirror holding plate  34 , the flat surface parts  34   o ,  34   o  have lower surfaces  34 - 1  finished to be flat surfaces and are provided with screw passing holes  34   a ,  34   a.    
         [0112]     Incidentally, the above-mentioned holding frame  32  is fixed using the lower surface  34 - 2  as a reference, and the above-mentioned holding frame  33  is fixed using the lower surfaces  34 - 1  as a reference.  
         [0113]     As shown in  FIGS. 7A and 7B , the left and right support pieces  35  and  36  symmetrical with each other in shape are provided at left and right end portions of the long holding frame  32 , for holding the plane mirror  31  so as to prevent it from coming off from the groove in the holding frame  32 .  
         [0114]     The support pieces will be described, taking the left support piece  35  as an example.  
         [0115]     As shown in  FIG. 21A , the left support piece  35  has a structure in which an upper surface  35 - 1  is provided with a plurality of reinforcement ribs  35   f  by plastic molding, and, as shown in  FIG. 21B , a lower face  35 - 2  is made to be a substantially flat surface, a side wall  35   a  is erectingly provided on the  35 - 2 , and a rectangular piece  35   c  is provided projectingly from the side wall  35   a  in parallel to the face  35 - 2 . In addition, roughly rectangular pieces  35   d ,  35   d  provided with screw passing holes  35   b ,  35   b  and a rectangular piece  35   e  are projectingly provided so that their faces on the upper side in  FIG. 21B  are stepped relative to the face  35 - 2 .  
         [0116]     Besides, the left support piece  35  is so held that its side of the face  35 - 2  in  FIG. 21B  is opposed to the side of a glass surface  31 - 2  of the above-mentioned plane mirror  31 , with a predetermined spacing therebetween.  
         [0117]     As shown in  FIG. 7A , two retainer pieces  37  are provided on each of the holding frames  32  and  33 , for holding the plane mirror  31  so as to prevent it from heavily chattering in the grooves in the holding frames  32  and  33 .  
         [0118]     As shown in  FIG. 21C , the retainer piece  37  is formed in a structure provided with a plurality of ribs, light in weight, and comparatively less liable to be deformed, from a plastic resin or the like. The retainer piece  37  is so formed that a step is formed between a lower face  37 - 1  on the side where roughly triangular reinforcement ribs  37   b  are provided on the viewer&#39;s side in  FIG. 21C  and a lower face  37 - 2  on the depth side where screw passing holes  37   c  and triangular reinforcement projected parts  37   a  are provided. This step is so sized that, when the retainer piece  37  is screwed to the holding frame  32  or  33  as shown in  FIG. 7A , a slight gap is formed between the glass surface  31 - 2  of the plane mirror  31  exposed on the upper side in  FIG. 7A  and the face  37 - 1 .  
         [0119]     As shown in  FIG. 7B , the shaft pieces  38 ,  38  and  39  is provided on the holding frame  32  on the side of the reflective surface  31 - 1  of the plane mirror  31  of the projection mirror  30 ; the shaft piece  39  is provided roughly at the center of the holding frame  32 , and the shaft pieces  38 ,  38  are provided at both end portions of the holding frame  32 .  
         [0120]     As shown in  FIG. 21D , the shaft pieces  38 ,  39  are each roughly semi-cylindrical in shape, and are each provided in the cylindrical side surface part thereof with three counter-sunk screw passing holes  38   b . Besides, in the shaft piece  38 , a slender shaft  38   a  is projectingly provided at the center of the semi-circle on one end side of the cylinder.  
         [0121]     In assembling the projection mirror  30  configured as above, first, the shaft pieces  38 ,  38  and  39  shown in  FIG. 7B  and the left support piece  35  are screwed to the holding frame  32 , and then the holding frame  32  is screwed to the mirror holding plate  34 . In this instance, the fixing by screws (screwing) is so conducted that the center line of the mirror holding plate  34  and the longitudinal direction of the holding frames  32  are orthogonal to each other.  
         [0122]     Next, in the condition where the mirror protective sheet  32   a  ( FIG. 20 ) is disposed at an end edge of the longer side of the plane mirror  31 , the plane mirror  31  is fitted into the angular U-shaped groove in the holding frame  32 , and one end on the side of the shorter side of the plane mirror  31  is put into abutment on the left support piece  35 . In this instance, the glass surface  31 - 2  is disposed on the side of the mirror holding plate  34 .  
         [0123]     Subsequently, the larger-width groove of the holding frame  33  is fitted over the plane mirror  31  with the mirror protective sheet  33   a  disposed at an end edge of a side parallel to the longer side thereof, and the holding frame  33  and the mirror holding plate  34  are fixed to each other by screws.  
         [0124]     Finally, the right support piece  36  is put into abutment on the other end on the side of the shorter side of the plane mirror  31 , and, in this condition, the right support piece  36  is screwed to the holding frame  32 .  
         [0125]     In this manner, the projection mirror  30  shown in  FIGS. 7A and 7B  is assembled.  
         [0126]     Now, the mounting of the projection mirror  30  assembled as shown in  FIGS. 7A and 7B  onto the frame structure body will be sequentially described below.  
         [0127]     First of all, the procedure of mounting the projection mirror  30  to the top frame  14  will be described.  
         [0128]     First, the two grips  34   c  of the mirror holding plate  34  are gripped by hands in the condition where the mirror holding plate  34  side of the projection mirror  30  is facing upward and the long holding frame  32  side of the projection mirror  30  is facing forward, as shown in  FIG. 7A .  
         [0129]     Then, in the condition where the mirror holding plate  34  is gripped, the projection mirror  30  is first lifted and moved toward a skewly upper side as indicated by arrow A in  FIG. 18 , in such a manner that the shaft pieces  38 ,  38  and  39  provided under the long holding frame  32  disposed on the front side abuts on the upper surface of the thick wall part  14   e  on the rear side of the drooping face  14 - 1  of the top frame  14 . Next, the projection mirror  30  is moved further in the direction of arrow A to cause the shaft pieces  38 ,  38  and  39  to ride over an upper surface portion of the thick wall part  14   e . Thereafter, the projection mirror  30  is lowered as indicated by arrow B, thereby fitting the shaft pieces  38 ,  38  and  39  into the cylindrical-surfaced recessed groove  14   a  in the top frame  14 .  
         [0130]     As a result, the projection mirror  30  is in a condition where the reflective surface  31 - 1  of the plane mirror  31  is facing down, and the holding frame  32  side is turnably engaged with the top frame  14 .  
         [0131]     Now, the mounting of the projection mirror  30  to the mirror fixing plate  19  and positional adjustment in this situation will be described below referring to  FIGS. 6, 16 ,  19 ,  22  and  23 .  
         [0132]     First, as shown in a partly broken perspective view in  FIG. 22 , the tentative support  20  (see  FIG. 16 ) is mounted on the mirror fixing plate  19 . Then, in the condition shown in  FIG. 22  where the holding frame  32  side of the projection mirror  30  is turnably mounted in the cylindrical-surfaced recessed groove  14   a  of the top frame  14 , a compression coil spring  40  is mounted in the spring guide  34   d  of the mirror holding plate  34 .  
         [0133]     Next, while holding the grips  34   c ,  34   c , the projection mirror  30  is turned so as to insert the engaging pawl  20   a  of the tentative support  20  into the roughly rectangular opening  34   h  in the mirror holding plate  34  (see  FIG. 19 ). In this instance, since the engageable part  34   f  of the mirror holding plate  34  is locked by the engaging pawl  20   a  of the tentative support  20 , the projection mirror  30  is maintained in a predetermined position even when the hands are put off the grips  34   c ,  34   c  of the mirror holding plate  34 .  
         [0134]     Subsequently, the adjusting screw  21  is passed through the round hole  20   b  in the tentative support  20  and the slot  19   f  in the mirror fixing plate  19 , and is screw-engaged into the screw hole  34   e  provided in the spring guide  34   d  of the mirror holding plate  34  (see  FIGS. 6, 19  and  22 ).  
         [0135]     Next, the screwing-in amount of the adjusting screw  21  is adjusted to an initial general position while using, for example, graduations provided on the engaging pawl  20   a  of the tentative pawl  20   a  as a yardstick (see  FIGS. 19 and 23 ). With this adjustment of the screwing-in amount, the turning amount of the top frame  14  of the projection mirror  30  around the cylindrical-surfaced recessed groove  14   a  can be finely adjusted.  
         [0136]     In this condition, the adjusting screw  21  is in screw engagement with the screw hole  34   e  in the mirror holding plate  34  by way of the compression coil spring  40 ; therefore, when the mirror support  17  side of the projection mirror  30  is lifted up, the movement is permitted until the spring guide  34   d  substantially abuts on the mirror fixing plate  19 . Incidentally, the adjustment in this stage may be rough, and a final adjustment is conducted upon assembly of the display unit  2  or in a site of installation of the display by the user.  
         [0137]     Subsequently, the fixing plate  22  is mounted to the mirror fixing plate  19 , and the fixing screw  23  is passed through the round hole  22   b  in the fixing plate  22  and the round hole  20   c  in the tentative support  20  and screw-engaged into the screw hole  19   g  in the mirror fixing plate  19 . This results in the condition shown in  FIGS. 19 and 23  where the fixing plate  22  and the mirror fixing plate  19  clamps the flange part  21   a  ( FIG. 16 ) of the adjusting screw  21  therebetween, to fix the adjusting screw  21  into a non-rotatable state.  
         [0138]     Incidentally,  FIG. 23  is a sectional perspective view showing the condition where the mounting of the projection mirror  30  is completed, in the same manner as  FIG. 19 , except that the plane mirror  31  as an essential part equipped with the adjusting screw  21  is omitted.  
         [0139]     In this manner, as shown in  FIGS. 6 and 19 , the mirror holding plate  34  of the projection mirror  30  is positionally adjusted and fixed relative to the mirror fixing plate  19  connecting the top frame  14  and the mirror support  17  to each other, and the inclination angle of the plane mirror  31  of the projection mirror  30  is set to a predetermined value.  
         [0140]     The display unit  2  in the rear projection display apparatus configured as above is assembled in the following manner.  
         [0141]     In the first place, as shown in  FIG. 5 , the optical unit  50  is mounted on the frame structure body shown in  FIG. 6 , using a positioning hole  11 - 4  provided in the bottom frame  11  as a reference. On the other hand, the projection mirror  30  shown in  FIG. 7A , in which the shaft pieces shown in  FIG. 7B  can be rotatingly slid inside the cylindrical-surfaced recessed groove  14   a  shown in  FIG. 11A  of the top frame  14 , is provided at a predetermined turning angle by the mirror fixing plate  19 . In this case, the projection mirror  30  can be turned through the engagement between the shafts  38   a ,  38   a  of the shaft pieces  38 ,  38  thereof and mirror bearings  2   a ,  2   b  shown in  FIG. 4  which are mounted at upper portions of the left and right side frames  12 ,  13 .  
         [0142]     Then, the screen  3  is mounted on the depth side in  FIG. 5  of the screen frame composed of the frames  11 ,  12 ,  13  and  14 , and peripheral parts of the screen  3  are retained by the four screen retainers  9   a ,  9   b ,  9   c  and  9   d  shown in  FIG. 4 .  
         [0143]     Incidentally, as shown in  FIG. 15 , the left and right retainers shown in  FIG. 4  for the screen  3  having a multi-layer structure are disposed on the side of the faces  12 - 1  and  13 - 1  of the left and right side frames  12  and  13  through an elastic damper sheet  3   a  therebetween, and the screen  3  is fixed so that the screen  3  is not deformed, by the left and right screen retainers  9   b  and  9   c . By the upper and lower screen retainers  9   a  and  9   d , also, the screen  3  is so fixed as not to be deformed (see  FIG. 4 ).  
         [0144]     As a result, the display unit  2  is assembled as shown in  FIG. 5  when viewed from the rear side, and as shown in  FIG. 4  when viewed from the front side. Then, the base part cover  7  is attached to the base part plate  25  fixed to the plate-like part  11   f  of the bottom frame  11 , from the front side of the display unit  2 , and the outer frame  4  and the cover frame  6  are disposed in position, as shown in  FIG. 3 ; in this condition, the rear cover  5  is screwed to the outer frame  4  from the rear side, so as to cover the optical unit  50  and the like. In fixing the cover frame  6  to the outer frame  4 , in the rear projection display apparatus according to this embodiment, the speaker units  8 ,  8  shown in  FIG. 2  are disposed in position.  
         [0145]     In this case, when the mirror adjusting part lid  5   a  provided at an upper portion of the rear cover  5  shown in  FIG. 2  is opened, the mirror fixing plate  19  shown in  FIG. 16  is exposed, so that the inclination angle of the projection mirror  30  can be finely adjusted by untightening the fixing screw  23  and rotating the adjusting screw  21 .  
         [0146]     Thus, in the rear projection display apparatus in this embodiment, in fixing the plane mirror  31 , the plane mirror  31  is fitted into the grooves in the holding frames  32  and  33  through the mirror protective sheets  32   a  and  33   a  ( FIG. 20 ) therebetween, and the four retainer pieces  37  and the left and right support pieces  35  and  33  made of plastic are arranged at the periphery of the plane mirror  31 , whereby the plane mirror  31  can be prevented from being broken due to direct contact with the holding frames  32  and  33  made of a metal ( FIG. 7 ).  
         [0147]     In addition, the holding frames  32  and  33  composed of extruded members of an aluminum alloy capable of being produced with high surface accuracy are mounted on the front and rear sides in  FIG. 7A  of the plane mirror  31 , and the holding frames  32  and  33  are fixed by the mirror holding plate  34  formed by die casting and finally finished with a high accuracy, whereby the plane mirror  31  can be held with a high flatness.  
         [0148]     Besides, the inclination angle of the plane mirror  31  can be adjusted by a method in which the angle of fixation of the mirror holding plate  34  to the mirror fixing plate  19  is changed by rotating the adjusting screw  21  screw-engaged, from the mirror fixing plate  19  side, into the screw hole  34   e  provided in the spring guide  34   d  on the mirror holding plate  34  side.  
         [0149]     Further, since the compression coil spring  40  is inserted between the mirror holding plate  34  and the mirror fixing plate  19  and a biasing force is exerted at all times on the adjusting screw  21  to obviate slackening, the position of the plane mirror  31  would not be deviated largely, even at the times of adjustment, transportation and use of the display.  
         [0150]     In addition, since the flange part  21   a  of the adjusting screw  21  is clamped between the fixing plate  22  and the mirror fixing plate  19  and fixed by the fixing screw  23  after the adjustment, the adjusting screw  21  is prevented from being rotated, with the result of generation of an error in the adjusted condition, in practical use of the display.  
         [0151]     Besides, since the grips integral with the mirror holding plate  34  are provided, operations conducted by holding the grips by hand can prevent the surface of the plane mirror  31  from being stained at the times of mounting and adjusting the projection mirror  30 . In addition, in mounting the projection mirror  30 , the mirror holding plate  34  is lifted up in a turning manner by holding the grips  34   c ,  34   c  of the mirror holding plate  34 , in the condition where the shaft pieces  38 ,  38 ,  39  are fitted in the cylindrical-surfaced recessed groove  14   a  of the top frame  14 . Then, the adjusting screw  21  is screw-engaged and fixed into the screw passing hole  34   b  in the mirror holding plate  34 , when the engageable part  34   f  of the mirror holding plate  34  is locked by the engaging pawl  20   a  of the tentative support  20 , whereby the projection mirror  30  is prevented from dropping, even when the hands are put off the grips  34   c ,  34   c . This structure promises enhanced workability and safety.  
         [0152]     Furthermore, the fine adjustment of the inclination angle of the projection mirror  30  can be carried out, as required, even after the rear projection display apparatus is assembled, by opening the mirror adjusting part lid  5   a  of the rear cover  5  shown in  FIG. 1  so as to expose the part of the mirror fixing plate  19 .  
         [0153]     According to the rear projection display apparatus in this embodiment, the inclination angle of the projection mirror can be finely adjusted by use of the small-pitch adjusting screw, which makes it possible to realize a reduced-thickness system in which an inclination angle with a higher accuracy may be required. In addition, fine adjustment of the inclination angle can be made by use of the adjusting screw for the projection mirror provided at the mirror fixing plate even after the assembled condition of the display, so that it is possible to easily coped with a need for re-adjustment which may be generated due to a shock during transportation, for example.  
         [0154]     Besides, since the projection mirror is provided with a simple structure in which the adjusting screw is screw-engaged from the mirror fixing plate side into the screw hole provided at a single position of the mirror holding plate and the inclination angle of the plane mirror is adjusted by only rotating the adjusting screw, an adjusting operation is facilitated, which contributes to suppression of cost.  
         [0155]     The rear projection display apparatus according to the present invention is not limited to the above-described embodiment, and other various configurations can naturally be adopted within the scope of the gist of the invention. For instance, while the reflection-type liquid crystal image display panel has been used as the optical system in the above embodiment, a transmission-type liquid crystal image display panel may also be used. Or, a configuration using an element for controlling a minute mirror such as a DLP (Digital Light Processing) type display panel may also be adopted. In addition, while the side supports as reinforcement for the frames have been provided on the left and right sides in the above embodiment, a configuration may be adopted in which a side support is provided on one of the left and right sides.  
         [0156]     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.