Abstract:
An image display apparatus includes a display element for displaying a video image, a backlight source for illuminating the display element, and a sculptured surface prism for guiding light from the display element. The sculptured surface prism enlarges the video image on the display element and presents the video image to an observer. The display element and the sculptured surface prism are supported by a holding member. An electrical circuit board is provided to drive the display element. The electrical circuit board and the display element are electrically connected. The electrical circuit board is arranged behind the display element, behind the sculptured surface prism when viewed from the observer, or on one side of the sculptured surface prism when viewed by the observer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image display apparatus such as a head mounted display which is mounted on the head to see a video image. 
     2. Related Background Art 
     Recently, image display apparatuses called head mounted displays (HMDS) which are mounted on the heads to see video images projected on display units are used for the purpose of seeing video images or screens of personal computers. 
     An HMD realizes appreciation of videos and the like anywhere without any influence on ambience. However, since it is mounted on the head, a demand has arisen for a lightweight apparatus with light fitting properties or a portable apparatus easy to detach. In addition, a portable facsimile image display apparatus which aims at seeing a facsimile image, or a portable image display apparatus such as a portable video phone has also been proposed. 
     As an HMD, an apparatus using a half mirror and concave mirror as an optical system and an LCD panel or a transmission liquid crystal display as a display element, which illuminates the LCD panel with backlight to see an image on the LCD panel is disclosed in Japanese Laid-Open Patent Application No. 8-251510. The present applicant has also proposed an optical system suitable for an HMD in Japanese Laid-Open Patent Application No. 7-104209. 
     As a portable image display apparatus, a transceiver having a small virtual image display is disclosed in Japanese Laid-Open Patent Application No. 7-235892. A display element and optical system suitable for this apparatus are disclosed in Japanese Laid-Open Patent Application No. 8-327920. 
     However, since the HMD disclosed in Japanese Laid-Open Patent Application No. 8-251510 uses a half mirror and concave mirror as an optical system, the optical system is large in the back-and-forth direction with respect to the line of sight. In addition, since the electrical circuit is arranged above the optical system, the dimension also becomes larger in the vertical direction to result in poor portability. This degrades the portability and makes it difficult to carry the apparatus in a pocket. Furthermore, since a half mirror is used, no bright screen display is possible. 
     In Japanese Laid-Open Patent Application No. 7-104209, an apparatus uses a sculptured surface prism to reduce the dimensions of the optical system and obtain light fitting properties. However, much improvement is required to carry the apparatus in a pocket or for portable use as an HMD. 
     In the portable image display apparatus disclosed in Japanese Laid-Open Patent Application No. 8-327920, since the optical system is formed by overlapping lenses in the direction of line of sight, and the electrical circuit board is arranged in the direction parallel to line of sight, the dimension in the back-and-forth direction becomes large. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an image display apparatus which solves the above-described problems and realizes small dimensions and excellent portability. 
     Other objects, features, and advantages of the present invention will become apparent from the following description of preferred embodiments in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing the first embodiment; 
     FIG. 2 is a sectional view showing the main part; 
     FIG. 3 is a sectional view showing the second embodiment; 
     FIG. 4 is a perspective view showing the third embodiment; 
     FIG. 5 is a sectional view of the main part; 
     FIG. 6 is a perspective view showing the fourth embodiment; 
     FIG. 7 is a perspective view showing a portable video phone of the fifth embodiment; 
     FIG. 8 is a perspective view showing the sixth embodiment; 
     FIG. 9 is a perspective view showing the main part; and 
     FIG. 10 is a perspective view showing the seventh embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the accompanying drawings. 
     FIG. 1 is a perspective view showing an image display apparatus according to the first embodiment. FIG. 2 is a sectional view. This image display apparatus mainly comprises transmission LCD panels  1 L and  1 R for displaying video images for the left and right eyes of a user, respectively, flat tube-type fluorescent backlight units  2 L and  2 R for illuminating the LCD panels  1 L and  1 R, respectively, sculptured surface prisms  3 L and  3 R for enlarging video images on the LCD panels  1 L and  1 R and projecting them onto the left and right eyes, respectively, and an electrical circuit board  4  for controlling the system. These members are compactly accommodated in cover members, i.e., a base cover  5  and lid cover  6  of, e.g., an ABS resin. 
     The LCD panels  1 L and  1 R and sculptured surface prisms  3 L and  3 R are supported by a holding member  7  formed from, e.g., a polycarbonate resin. The holding member  7  has attachment surfaces  8 L and  8 R for attaching the LCD panels  1 L and  1 R for left and right eyes. The attachment surfaces  8 L and  8 R have openings  9 L and  9 R, respectively. A board attachment boss  10  projects upward between the attachment surfaces  8 L and  8 R. 
     The LCD panels  1 L and  1 R are positioned such that predetermined relationships hold between the LCD panels  1 L and  1 R and sculptured surface prisms  3 L and  3 R, respectively, the display portions are positioned in the ranges of the openings  9 L and  9 R of the holding member  7 , and the user can obtain a natural view in observation, and fixed on the attachment surfaces  8 L and  8 R of the holding member  7  by bonding or screwing. 
     A total of four attachment flanges  11 LL and  11 LR, and  11 RL and  11 RR (attachment flanges  11 LR and  11 RR are not shown) are vertically formed at the two ends of the openings  9 L and  9 R on the lower side of the attachment surfaces  8 L and  8 R, respectively. A rib vertically formed between the attachment flanges  11 LR and  11 RL has an attachment hole  12  (not shown). 
     The sculptured surface prisms  3 L and  3 R are formed from, e.g., an acrylic resin and have optical characteristics as disclosed in Japanese Laid-Open Patent Application No. 7-104209. A total of four attachment flanges  13 LL and  13 LR, and  13 RL and  13 RR (attachment flanges  13 LR and  13 RR are not shown) are formed integrally with the side surfaces of the sculptured surface prisms  3 L and  3 R, respectively. The sculptured surface prisms  3 L and  3 R are positioned and fixed to the holding member  107  by bonding or screwing while making the attachment flanges  13 LL,  13 LR,  13 RL, and  13 RR correspond to the attachment flanges  11 LL,  11 LR,  11 RL, and  11 RR of the holding member  7 , respectively. 
     The backlight units  2 L and  2 R are fixed on the LCD panels  1 L and  1 R, respectively, via a spacer or the like by a known means such as bonding. The electrical circuit board  4  having a drive circuit is mounted on the backlight units  2 L and  2 R. The backlight units  2 L and  2 R are electrically connected to electrode patterns on the electrical circuit board by soldering. 
     Electrodes for driving the backlight units  2 L and  2 R are connected to the electrical circuit board  4  through flexible flat cables  14 L and  14 R, respectively. The flexible flat cables  14 L and  14 R are bent, e.g., once with a margin such that the LCD panels  1 L and  1 R can be moved in positioning them. 
     The electrical circuit board  4  is formed from, e.g., a multilayered glass epoxy board and has an attachment hole  15  at substantially the central portion. The electrical circuit board  4  is fixed to the board attachment boss  10  of the holding member  7  through the attachment hole  15  by a screw. Circuits for displaying video images on the LCD panels  1 L and  1 R, inverter circuits for turning on the backlight units  2 L and  2 R, and power supply circuit are formed on the electrical circuit board  4 . These circuits are connected to a video signal generation means such as a video deck including a video output circuit, signal processing circuit, and power supply circuit through an electrical wire  16  and a connector. The intermediate layer of the electrical circuit board  4  is partially grounded as a shield layer, so a high voltage generated in the inverter circuits is prevented from adversely affecting the video processing circuit as noise. 
     An attachment boss  17  projects at the center of the base cover  5  as a cover member. Openings  18 L and  18 R for left and right eyes are formed on the left and right sides of the attachment boss  17 . The attachment boss  17  has a screw hole at the center. The holding member  7  is fixed to the base cover  5  by screwing the base cover  5  through the attachment hole  12  of the holding member  7 . A damping member such as a rubber bush is inserted between the attachment hole  12  of the holding member  7  and the attachment boss  17  of the base cover  5 , so that the holding member  7  is prevented from being deformed by an external force applied to the base cover  5  to impede a natural view. 
     The base cover  5  and lid cover  6  are fixed by bonding or screwing while a bush  19  attached to the electrical wire  16  is sandwiched between a notch  20  of the base cover  5  and a notch  21  of the lid cover  6  to mechanically fix the electrical wire  16 . 
     The user mounts the image display apparatus with this arrangement on the head and looks in through the openings  18 L and  18 R of the base cover  5 . Video signals from the video output device are output to the LCD panels  1 L and  1 R. Video images on the LCD panels  1 L and  1 R illuminated with the backlight units  2 L and  2 R are enlarged through the sculptured surface prisms  3 L and  3 R and observed by the user. 
     Since the image display apparatus of this embodiment has an efficient component arrangement: for example, the electrical circuit board  4  is positioned behind the LCD panels  1 L and  1 R, as shown in FIG.  2 . Hence, the apparatus can be made compact. In assembly, the flexible flat cables  14 L and  14 R have slack and are bent at least once. For this reason, even when the LCD panels  1 L and  1 R move in positioning, the holding member  7  can be prevented from being applied with a force and deformed, and the LCD panels  1 L and  1 R can be prevented from shifting to adversely affect the video image. Since the electrical circuit board  4  is fixed to the holding member  7  at only substantially the central portion, the holding member  7  can be prevented from deforming due to the shape and, more particularly, the flatness of the electrical circuit board  4 , so the user can obtain a natural view. 
     In this embodiment, the inverter circuits for turning on the fluorescent backlight units  2 L and  2 R are also formed on the electrical circuit board  4 . When noise poses a problem, the inverter circuits are preferably formed on another board and arranged behind the backlight units. 
     FIG. 3 is a sectional view showing the arrangement of the second embodiment. The electrical circuit board of the first embodiment is a hard plate such as a glass epoxy board. In the second embodiment, the electrical circuit board is formed from a flexible printed board and positioned and fixed to a cover member, thereby making the entire apparatus more compact. The basic arrangement is almost the same as in the first embodiment. The same reference numerals as in the first embodiment denote the same parts in the second embodiment. 
     An electrical circuit board  30  is formed from a flexible printed board using, e.g., a polyimide resin as a base, and electrically connected to LCD panels  1 L and  1 R through flexible flat cables  14 L and  14 R integrated with the LCD panels  1 L and  1 R. Backlight units  2 L and.  2 R are connected and fixed to the electrical circuit board  30  at positions opposing the LCD panels  1 L and  1 R by soldering. On the flat portion of the electrical circuit board  30 , circuits connected to a video signal generation means through an electrical wire  16  to display signals from the video signal generation means on the LCD panels  1 L and  1 R, inverter circuits for turning on the backlight units, and power supply circuit are formed, as in the first embodiment. 
     The electrical circuit board  30  has four attachment holes  31 LL,  31 LR,  31 RL, and  31 RR (attachment holes  31 RL and  31 RR are not shown). A lid cover  6  as a cover member has, on its inner surface, four attachment dowels  32 LL,  32 LR,  32 RL, and  32 RR (attachment dowels  32 RL and  32 RR are not shown) for positioning and fixing the electrical circuit board  30 . In assembling the apparatus, the attachment dowels  32 LL,  32 LR,  32 RL, and  32 RR are fitted in the attachment holes  31 LL,  31 LR,  31 RL, and  31 RR of the electrical circuit board  30 , respectively, and the electrical circuit board  30  is fixed to the lid cover  6  by screwing or the like. 
     Since the interval between the attachment dowels  32 LL,  32 LR,  32 RL, and  32 RR having directional components perpendicular to the viewing surface is made smaller than that between the attachment holes  31 LL,  31 LR,  31 RL, and  31 RR of the electrical circuit board  30  by a predetermined amount, the electrical circuit board  30  is fixed to the lid cover  6  by the elasticity of the electrical circuit board  30  formed from a flexible flat cable. 
     With this arrangement, the user mounts the image display apparatus on the head and looks in through openings  18 L and  18 R of a base cover  5 . Video signals from the video output device are output to the LCD panels  1 L and  1 R. The video images on the LCD panels  1 L and  1 R illuminated with the backlight units  2 L and  2 R are enlarged through sculptured surface prisms  3 L and  3 R and observed by the user. 
     Since the electrical circuit board  30  in the image display apparatus is set along the inner wall of the lid cover  6  in assembling, the apparatus can be made compact. In addition, since the electrical circuit board  30  is formed from a flexible flat cable, it can be folded to concentrate circuit components of integrated circuits in the space between the LCD panels  1 L and  1 R and between the backlight units  2 L and  2 R for left and right eyes. Hence, the apparatus can be made more compact. 
     The image display apparatus of this embodiment has no mount portion, and the user holds the image display apparatus with a hand and looks in through the openings  18 L and  18 R of the base cover  5 . However, when the mount mechanism of an HMD is attached to the base cover  5 , the image.display apparatus can also be used as an HMD. 
     FIG. 4 is a perspective view showing an image display apparatus according to the third embodiment. FIG. 5 is a sectional view. This will be described below although the description is partially the same as in the above embodiments. This image display apparatus mainly comprises transmission LCD panels  101 L and  101 R for displaying video images for the left and right eyes of a user, respectively, backlight units  102 L and  102 R for illuminating the LCD panels  1 L and  1 R, respectively, sculptured surface prisms  103 L and  103 R for enlarging video images on the LCD panels  101 L and  101 R and projecting them onto the left and right eyes, respectively, and an electrical circuit board  104  for controlling the system. These members are compactly accommodated in cover members, i.e., a base cover  5  and lid cover  6  of, e.g., an ABS resin. 
     The LCD panels  101 L and  101 R and sculptured surface prisms  103 L and  103 R are supported by a holding member  107  formed from, e.g., a polycarbonate resin. For the holding member  107 , attachment surfaces  108 L and  108 R for attaching the LCD panels  101 L and  101 R for left and right eyes are coupled by a vertical surface  109 . The attachment surfaces  108 L and  108 R have openings  10 L and  110 R at their central portions, respectively. 
     The LCD panels  101 L and  101 R are positioned such that predetermined relationships hold between the LCD panels  101 L and  101 R and sculptured surface prisms  103 L and  103 R, respectively, the display portions are positioned in the ranges of the openings  110 L and  110 R of the holding member  107 , so that the user can obtain a natural view in observation, and the display portions are fixed on the attachment surfaces  108 L and  108 R of the holding member  107  by bonding or screwing. 
     A total of four attachment flanges  111 LL and  111 LR, and  111 RL and  111 RR (attachment flanges  111 LR and  111 RR are not shown) are vertically formed at two ends of the openings  110 L and  110 R on the lower side of the attachment surfaces  108 L and  108 R, respectively. The vertical surface  109  has an attachment hole  112  and attachment boss  113  at the upper and lower portions, respectively. 
     The sculptured surface prisms  103 L and  103 R are formed from e.g., an acrylic resin and have optical characteristics as disclosed in Japanese Laid-Open Patent Application No. 7-104209. A total of four attachment flanges  114 LL and  114 LR, and  114 RL and  114 RR (attachment flanges  114 LR and  114 RR are not shown) are formed integrally with the side surfaces of the sculptured surface prisms  103 L and  103 R, respectively. The sculptured surface prisms  103 L and  103 R are positioned and fixed to the holding member  107  by bonding or screwing while making the attachment flanges  114 LL,  114 LR,  114 RL, and  114 RR correspond to the attachment flanges  111 LL,  111 LR,  111 RL, and  111 RR of the holding member  107 , respectively. 
     Electrodes for driving the LCD panels  101 L and  101 R are connected to the electrical circuit board  104  with drive circuits through flexible flat cables  115 L and  115 R, respectively. Each of the flexible flat cables  115 L and  115 R has, e.g., an S shape bent twice such that the LCD panels  101 L and  101 R can be moved in positioning them. 
     The electrical circuit board  104  is formed from, e.g., a glass epoxy board and has an attachment hole  116  at substantially the central portion. The electrical circuit board  104  is fixed to the attachment boss  113  of the holding member  107  through the attachment hole  116  by a screw. Circuits for displaying video images on the LCD panels  101 L and  101 R, inverter circuits for turning on the backlight units  102 L and  102 R, and power supply circuit are formed on the electrical circuit board  104 . These circuits are connected to a video signal generation means such as a video deck including a video output circuit, signal processing circuit, and power supply circuit through an electrical wire  117  and a connector. 
     The backlight units  102 L and  102 R are formed from flat tube-type fluorescent backlight units  118 L and  118 R and inverter circuits  119 L and  119 R, respectively. The backlight units  102 L and  102 R are fixed on the LCD panels  101 L and  101 R via a spacer by a known means such as bonding and connected to the electrical circuits on the electrical circuit board  104  through electrical wires  120 L and  120 R, respectively. 
     The base cover  105  as a cover member has an attachment boss  121  at the center, and openings  122 L and  122 R for left and right eyes are formed on the left and right sides of the attachment boss  121 . The attachment boss  121  has a screw hole at the center. The holding member  107  is fixed to the base cover  105  by screwing the base cover  105  through the attachment hole  112  of the holding member  107 . A damping member such as a rubber bush is inserted between the attachment hole  112  of the holding member  107  and the attachment boss  121  of the base cover  105 , so that the holding member  107  is prevented from being deformed by an external force applied to the base cover  105  to impede a natural view. The base cover  105  and lid cover  106  are fixed by bonding or screwing while a bush  123  attached to the electrical wire  117  is sandwiched between a notch  124  of the base cover  105  and a notch  125  of the lid cover  106  to mechanically fix the electrical wire  117 . 
     With this arrangement, video images corresponding to video signals from the video output device are displayed on the LCD panels  101 L and  101 R. The video images on the LCD panels  101 L and  101 R illuminated with the backlight units  118 L and  118 R are enlarged through sculptured surface prisms  103 L and  103 R and observed by the user through the openings  122 L and  122 R of the base cover  105 . 
     Since the image display apparatus of this embodiment has an efficient component arrangement: for example, the electrical circuit board  104  is positioned behind the sculptured surface prisms  103 L and  103 R, as shown in FIG.  5 . Hence, the apparatus can be made compact. In assembly, the flexible flat cables  115 L and  115 R have slack and are bent at least once. For this reason, even when the LCD panels  101 L and  101 R move in positioning, the holding member  107  can be prevented from being applied with a force and deformed, and the LCD panels  101 L and  101 R can be prevented from shifting to adversely affect the video image. Since the electrical circuit board  104  is fixed to the holding member  107  at only substantially the central portion, the holding member  107  can be prevented from deforming due to the accuracy of the shape and, more particularly, flatness of the electrical circuit board  104 , so the user can obtain a natural view. 
     In the third embodiment, the inverter circuits  119 L and  119 R are constructed as the backlight units  102 L and  102 R together with the fluorescent backlight units  118 L and  118 R. However, the inverter circuits  119 L and  119 R may be formed on the electrical circuit board  104 . In this case, to prevent noise, the electrical circuit board  104  and the LCD panels  101 L and  101 R are preferably connected by cables different from those for connecting the fluorescent backlight units  118 L and  118 R. 
     FIG. 6 is a perspective view of an image display apparatus according to the fourth embodiment, which can be applied to a portable video phone or facsimile viewer. This image display apparatus mainly comprises a transmission LCD panel  130  for a single eye, backlight unit  131 , and sculptured surface prism  132 . These members are accommodated in cover members, i.e., a base cover  134  and lid cover  135  together with an electrical circuit board  133 . 
     A holding member  136  of this embodiment is also formed from, e.g., a polycarbonate resin. The holding member  136  has an opening  137 , LCD attachment surface  138 , attachment holes  139 L and  139 R, and attachment flanges  140 L and  140 R. The sculptured surface prism  132  is the same as in the third embodiment and has left and right attachment screw holes in the surface opposing the LCD panel  130  outside the range where effective light passes through. When screws  141 L and  141 R are driven into the screw holes through the attachment holes  139 L and  139 R of the holding member  136 , the sculptured surface prism  132  is fixed on the lower side of the holding member  136 . 
     The LCD panel  130  is fixed on the LCD attachment surface  138  of the holding member  136  by bonding or screwing such that a predetermined relationship holds between the LCD panel  130  and sculptured surface prism  132 , and the display portion is positioned within the range of the opening  137  of the holding member  136 . An electrode for driving the LCD panel  130  is connected to the electrical circuit board  133  having an attachment hole  143 , on which the drive circuit is formed, through a flexible flat cable  142 . 
     The electrical circuit board  133  is connected to a video signal generation means through an electrical wire  144  and connector. The backlight unit  131  is formed from a fluorescent backlight unit  145  and inverter circuit  146 . The backlight unit  131  is fixed to the LCD panel  130  via a spacer by a known means such as bonding, and also connected to the electrical circuit board  133  through an electrical wire  147 . 
     The base cover  134  has an opening  148  and attachment bosses  149 L and  149 R. The attachment bosses  149 L and  149 R have screw holes at their centers. When screws are driven into the screw holes through the attachment flanges  140 L and  140 R of the holding member  136 , the holding member  136  is fixed to the base cover  134 . 
     The lid cover  135  has a board attachment boss  150 . When the board attachment boss  150  is inserted into the attachment hole  143  of the electrical circuit board  133 , and a screw is driven into the screw hole of the board attachment boss  150 , the electrical circuit board  133  is fixed to the lid cover  135 . The lid cover  135  is further fixed to the base cover  134  by a known means such as bonding or screwing. At this time, a bush  151  attached to the electrical wire  144  is sandwiched by notches  152  and  153  of the base cover  134  and lid cover  135 . 
     With this arrangement, a video signal from the video output device is output to the LCD panel  130 . The video image on the LCD panel  130  illuminated with the backlight unit  131  is enlarged through the sculptured surface prism  132  and observed by one eye of the user who is looking from the opening  148  of the base cover  134 . As described above, when the electrical circuit board  133  is fixed to the top case  135 , the holding member  136  can be prevented from being deformed in fixing the electrical circuit board  133 . 
     FIG. 7 shows the fifth embodiment in which a single-eye image display apparatus is applied to a portable video phone. A visual unit  156  for displaying an image is connected to a portable telephone main body  155 . More specifically, the image display apparatus shown in FIG. 6 is electrically connected to the portable telephone main body  155  and mechanically fixed. In this case, to cope with the personal difference in head shape between users, the visual unit  156  is preferably fixed such that it can pivot with respect to the portable telephone main body  155  at least in the vertical direction of the screen. 
     FIG. 8 is a perspective view showing the sixth embodiment. FIG. 9 is a sectional view. An electrical circuit board is formed not from a hard board but from a flexible printed board as part of a flexible flat cable to make the entire apparatus more compact, and this arrangement is applied to an HMD. 
     The image display apparatus of this embodiment comprises transmission LCD panels  160 L and  160 R for left and right eyes, backlight units  161 L and  161 R, and sculptured surface prisms  162 L and  162 R, as in the third embodiment. An electrical circuit board  163  is formed from the same material as that of a flexible flat cable, e.g., a polyimide resin, and integrated with the flexible flat cable. These members are compactly accommodated in cover members, i.e., a base cover  164  and lid cover  165 , as in the third embodiment. The base cover  164  has an HMD mount portion  166  for mounting the HMD on the head of a user. 
     A holding member  167  of this embodiment is also formed from, e.g., a polycarbonate resin. The front surface of the holding member  167  corresponds to an attachment surface for attaching the LCDs for left and right eyes, and the rear surface corresponds to a flat prism attachment surface for attaching the prisms for left and right eyes. The holding member  167  has openings  168 L and  168 R for left and right eyes. Prism attachment holes  169 LL and  169 LR, and  169 RL and  169 RR are formed on the left and right sides of the openings  168 L and  168 R, respectively. An attachment hole  171  for fixing the holding member  167  to the base cover  164  is formed in a vertical surface  170  at the central portion. 
     The sculptured surface prisms  162 L and  162 R are formed from, e.g., an acrylic resin and have the same optical characteristics as those of the third embodiment. Attachment surfaces  173 L and  173 R are formed on surfaces of the sculptured surface prisms  162 L and  162 R opposing the LCD panels  160 L and  160 R so as to surround regions  172 L and  172 R where effective light passes through. The attachment surfaces  173 L and  173 R have attachment screw holes  174 LL,  174 LR,  174 RL, and  174 RR, respectively. 
     The attachment surfaces  173 L and  173 R of the sculptured surface prisms abut against the prism attachment surface of the holding member  167 . When screws  175 LL,  175 LR,  175 RL, and  175 RR (screws  175 RL and  175 RR are not shown) are driven into the screw holes  174 LL,  174 LR,  174 RL, and  174 RR of the sculptured surface prisms  162 L and  162 R through the prism attachment holes  169 LL,  169 LR,  169 RL, and  169 RR, respectively, the sculptured surface prisms  162 L and  162 R are fixed to the holding member  167 . The position of the prism attachment surface is adjusted such that when the attachment surfaces  173 L and  173 R of the sculptured surface prisms  162 L and  162 R abut against the prism attachment surface of the holding member  167 , images on the LCD panels  160 L and  160 R can be seen as if they were separated from the user by, e.g., 2 m. 
     Also, for the sculptured surface prisms  162 L and  162 R and holding member  167 , a plurality of, e.g., two positioning bosses are formed on the attachment surfaces  173 L and  173 R (attachment surface  173 R is not shown) of the sculptured surface prisms  162 L and  162 R. Positioning holes corresponding to the bosses are formed in the prism attachment surface of the holding member  167 . The bosses are fitted in the positioning holes to position the sculptured surface prisms  162 L and  162 R in a direction perpendicular to the visual axis and fixed. 
     The electrical circuit board  163  has expanded portions  176 L and  176 R functioning as flexible flat cables. Each of the expanded portions  176 L and  176 R has an S shape bent twice, as shown in FIG. 8, such that the LCD panels  160 L and  160 R can be moved in positioning them. 
     The electrical circuit board  163  has attachment holes  177 LL,  177 LR,  177 RL, and  177 RR. Circuits for displaying signals from a video signal generation means on the LCD panels  160 L and  160 R, circuits for turning on the backlight units, and power supply circuit are formed on flat portions  178   a  and  178   b  on the electrical circuit board  163 . The electrical circuit board  163  is connected to the video signal generation means through an electrical wire  179 . 
     The base cover  164  has openings  180 L and  180 R and attachment boss  181 . The attachment boss  181  is inserted into the attachment hole  171  of the holding member  167  via a damping member such as a rubber bush is inserted, and a screw is driven into the screw hole formed at the center of the attachment boss  181 , thereby fixing the holding member  167  to the base cover  164 . 
     The lid cover  165  has four dowels  182 LL,  182 LR,  182 RL, and  182 RR (dowels  182 RL and  182 RR are not shown) for positioning and fixing the electrical circuit board  163 . In assembling the apparatus, the dowels  182 LL,  182 LR,  182 RL, and  182 RR are fitted in the four attachment holes  177 LL,  177 LR,  177 RL, and  177 RR of the electrical circuit board  163 , respectively, as shown in FIG. 9, to fix the electrical circuit board  163  to the lid cover  165 . 
     When the interval between the dowels  182 LL,  182 LR,  182 RL, and  182 RR formed in the vertical direction with respect to the line of sight is made smaller than that between the corresponding holes on the electrical circuit board  163  by a predetermined amount, the electrical circuit board  163  can be fixed to the lid cover  165  by the elastic force generated in the electrical circuit board  163 . The lid cover  165  is fixed to the lid cover  165  by a known means such as bonding or screwing. The electrical wire  179  is fixed while a bush  183  is sandwiched between the notch of the base cover  164  and notch of the lid cover  165 . 
     The HMD mount portion  166  is attached to the base cover  164  via an HMD mount portion attachment portion  184 . The HMD mount portion  166  comprises a front frame  185 , left and right side frames  186 L and  186 R, front pad  187 , and left and right hinges  188 L and  188 R. In the non-use state, the HMD mount portion  166  can be retracted by folding the left and right side frames  186 L and  186 R at the left and right hinges  188 L and  188 R. 
     With this arrangement, the user mounts the image display apparatus on the head using the front pad  187  and side frames  186 L and  186 R. Video signals are output from the video output device to the LCD panels  160 L and  160 R. Images on the LCD panels  160 L and  160 R illuminated with the backlight units  161 L and  161 R are enlarged through the sculptured surface prisms  162 L and  162 R and observed by the user through the openings  180 L and  180 R. 
     As described above, by fixing the sculptured surface prisms  162 L and  162 R to the holding member  167  and fixing the LCD panels  160 L and  160 R to the holding member  167 , dust can be prevented from entering the LCD panels  160 L and  160 R or surfaces of the sculptured surface prisms  162 L and  162 R opposing the LCD panels  160 L and  160 R. When a high optical magnification is set, a gap between the attachment surfaces  173 L and  173 R of the sculptured surface prisms  162 L and  162 R and holding member  167 , a gap between the LCD attachment surface  174  of the holding member  167  and LCD panels  160 L and  160 R, or a gap at a portion between the holding member  167  for fixing the LCD panels  160 L and  160 R and LCD panels  160 L and  160 R, which is not associated with display, is filled with a filler. In this case, small gaps formed depending on the surface states of components can be filled. For this reason, dust can be prevented from entering the gaps or being seen by the user when he/she looks at an image. 
     Since the electrical circuit board  163  shown in FIG. 9 is set along the inner wall of the lid cover  165  in assembling, the image display apparatus can be made compact. In addition, when the board and flat cables are laid out such that tall electrical components such as integrated circuits are positioned in the space between the sculptured surface prisms  162 L and  162 R, the apparatus can be made more compact. 
     FIG. 10 is a perspective view showing an image display apparatus according to the seventh embodiment. This image display apparatus mainly comprises transmission LCD panels  201 L and  201 R for displaying video images for the left and right eyes of a user, backlight units  202 L and  202 R for illuminating the LCD panels  201 L and  201 R, respectively, sculptured surface prisms  203 L and  203 R for enlarging video images on the LCD panels  201 L and  201 R and projecting them to left and right eyes, respectively, and an electrical circuit board  204  for controlling the system. These members are compactly accommodated in cover members, i.e., a base cover  205  and lid cover  206  formed from, e.g., an ABS resin. 
     The LCD panels  201 L and  201 R and sculptured surface prisms  203 L and  203 R are supported by a holding member  207  formed from, e.g., a polycarbonate resin. For the holding member  207 , attachment surfaces  208 L and  208 R for attaching the LCD panels  201 L and  201 R for left and right eyes are coupled by a vertical surface  209 . The attachment surfaces  208 L and  208 R have openings  210 L and  210 R at their central portions. 
     The LCD panels  201 L and  201 R are positioned such that predetermined relationships hold between the LCD panels  201 L and  201 R and sculptured surface prisms  203 L and  203 R, respectively, the display portions are positioned in the ranges of the openings  210 L and  210 R of the holding member  207 , and the user can obtain a natural view in observation, and fixed on the attachment surfaces  208 L and  208 R of the holding member  207  by bonding or screwing. 
     A total of four attachment flanges  211 LL and  211 LR, and  211 RL and  211 RR (attachment flanges  211 LR and  211 RR are not shown) are vertically formed at two ends of the openings  210 L and  210 R on the lower side of the attachment surfaces  208 L and  208 R, respectively. The vertical surface  209  has an attachment hole  212 . 
     The sculptured surface prisms  203 L and  203 R are formed from, e.g., an acrylic resin and has optical characteristics as disclosed in Japanese Laid-Open Patent Application No. 7-104209. A total of four attachment flanges  213 LL and  213 LR, and  213 RL and  213 RR (attachment flanges  213 LR and  213 RR are not shown) are formed integrally with the side surfaces of the sculptured surface prisms  203 L and  203 R, respectively. The sculptured surface prisms  203 L and  203 R are positioned and fixed to the holding member  207  by bonding or screwing while making the attachment flanges  213 LL,  213 LR,  213 RL, and  213 RR correspond to t he attachment flanges  211 LL,  211 LR,  211 RL, and  211 RR of the holding member  207 , respectively. 
     Electrodes for driving the LCD panels  201 L and  201 R are connected to the electrical circuit board  204  with drive circuits through flexible flat cables  214 L and  214 R, respectively. Each of the flexible flat cables  214 L and  214 R is bent and connected to the electrical circuit board  204  fixed on one side of the holding member  207 . 
     The electrical circuit board  204  is formed from, e.g., a glass epoxy board and has an attachment hole  215 . The electrical circuit board  204  is fixed to an attachment boss  217  of the holding member  207  through the attachment hole  215  by a screw  216 . Circuits for displaying video images on the LCD panels  201 L and  201 R, circuits for turning on the backlight units  202 L and  202 R, and power supply circuit are formed on the electrical circuit board  204 . These circuits are connected to a video signal generation means such as a video deck including a video output circuit, signal processing circuit, and power supply circuit through an electrical wire  218  and a connector. 
     The backlight units  202 L and  202 R comprise flat tube-type fluorescent backlight units  219 L and  219 R and inverter circuits  220 L and  220 R, respectively. The backlight units  202 L and  202 R are fixed on the LCD panels  201 L and  201 R via a spacer by a known means such as bonding and connected to the electrical circuits on the electrical circuit board  204  through electrical wires  221 L and  221 R, respectively. 
     The base cover  205  as a cover member has an attachment boss  222  at the center, and openings  223 L and  223 R for left and right eyes are formed on the left and right sides of the attachment boss  222 . The attachment boss  222  has a screw hole at the center. The holding member  207  is fixed to the base cover  205  by screwing the base cover  205  through the attachment hole  212  of the holding member  207 . A damping member such as a rubber bush is inserted between the attachment hole  212  of the holding member  207  and the attachment boss  222  of the base cover  205 , so that the holding member  207  is prevented from being deformed by an external force applied to the base cover  205  to impede a natural view. The base cover  205  and lid cover  206  are fixed by bonding or screwing while a bush  224  attached to the electrical wire  218  is sandwiched between a notch  225  of the base cover  205  and a notch  225  of the lid cover  206 . 
     With this arrangement, video images corresponding to video signals from the video output device are displayed on the LCD panels  201 L and  201 R. The video images on the LCD panels  201 L and  201 R illuminated with the backlight units  219 L and  219 R are enlarged through sculptured surface prisms  203 L and  203 R and observed by the user through the openings  223 L and  223 R of the base cover  205 . 
     Since the component arrangement is efficient: for example, the electrical circuit board  204  is positioned on one side of the sculptured surface prisms  203 L and  203 R. Hence, the apparatus can be made compact. In assembly, the LCD panels  201 L and  201 R and electrical circuit board  204  are separated by the flexible flat cables  214 L and  214 R. For this reason, even when the LCD panels  201 L and  201 R move in positioning, the holding member  207  can be prevented from being applied with a force and deformed, and the LCD panels  201 L and  201 R can be prevented from shifting to adversely affect the video image. Since the electrical circuit board  204  is fixed to the side surface of the holding member  207 , the holding member  207  can be prevented from deforming due to the shape and, more particularly, flatness of the electrical circuit board  204 , so the user can obtain a natural view. 
     In this embodiment, the inverter circuits  220 L and  220 R are constructed as the backlight units  202 L and  202 R together with the fluorescent backlight units  219 L and  219 R. However, the inverter circuits  220 L and  220 R may be formed on the electrical circuit board  204 . In this case, to prevent noise, the electrical circuit board  204  and the LCD panels  201 L and  201 R are preferably connected by cables different from those for connecting the fluorescent backlight units  219 L and  219 R. 
     In addition, in this embodiment, one electrical circuit board  204  having circuits for displaying video images on the left and right LCD panels  201 L and  201 R is disposed on one side of the image display apparatus. However, two electrical circuit boards  204  may be arranged on the left and right sides, respectively. Especially, when the scale of the electrical circuit board  204  is large, this arrangement can be employed to improve the portability of the image display apparatus. 
     In the seventh embodiment, fitting properties as an HMD have not been mentioned. When a mount unit as disclosed in Japanese Patent Application No. 10-14972 by the present applicant is attached to the base cover  205 , a compact apparatus as an HMD excellent in portability can be obtained. 
     In the image display apparatus of each of above embodiments, sculptured surface prisms are used as an optical system, an electrical circuit board is arranged on one side of the sculptured surface prisms, and the electrical circuit board and display elements are connected through flexible flat cables. With this arrangement, a compact apparatus excellent in portability can be realized. 
     When sculptured surface prisms for left and right eyes are used, an electrical circuit board is arranged on one side of the sculptured surface prisms, and the electrical circuit board and display elements for left and right eyes are connected through flexible flat cables, the visual axis can be prevented from shifting in the vertical direction due to bend of the flexible flat cables in assembling to adversely affect the optical condition. Hence, a safety, comfortable, and natural binocular can be realized.