Patent ID: 7142242

Claim:
An image forming optical device for forming an image of optical light from outside on a predetermined position, comprising: a first optical element of a prism shape having a first interface to pass through the optical light, a first reflect interface to reflect the optical light from the first interface, and a first output interface to output the optical light reflected from the first reflect interface; a second optical element of the same prism shape as the first optical element having a second interface to pass through the optical light from the first output interface, a second reflect interface to reflect the optical light from the second interface, and a second output interface to output the optical light reflected from the second reflect interface outside and to form an image of the optical light on a predetermined position; wherein, at least two of the six interfaces including the first and second interfaces, the first and second reflect interfaces and the first and second output interfaces are formed in a lens shape having a predetermined curved surface, and wherein an optical axis of the optical light passing through the first optical element and another optical axis of the optical light passing though the second optical element are in one plane, and wherein the optical axis of the optical light passing through the first interface is parallel to the other optical axis of the optical light passing through the second output interface, the first and second optical elements further having a protrusion for positioning a direction of the two optical axes in one plane and a rotative direction of the first and second optical elements respectively, wherein the protrusion is provided on surfaces of the first and second optical elements in parallel with the one plane and away from the optical axes so as to be perpendicular to the first interface and the second interface respectively.