Patent ID: 7075054

Claim:
An optical position detecting device comprising: a light retro-reflector provided outside a predetermined region; at least two optical transceivers, each including an optical scanning unit for angularly scanning light in a plane substantially parallel to the predetermined region and a light receiving unit for receiving reflected light from a portion of said light retro-reflector irradiated with the scanning light; and a detector for detecting presence of a light blocking object in a region optically scanned by said optical scanning units when a level of light received by said light receiving unit is lower than a predetermined first level and for detecting a position of the light blocking object based on scanning angles of said optical scanning units in this scanning, said optical position detecting device being characterized by further comprising: a comparing unit for comparing the level of light received by said light receiving unit with a second level higher than the first level; and a judging unit for making a judgment that said light retro-reflector is dirty when the level of light received by said light receiving unit is higher than the first level and lower than the second level.