Distance measurement system with light diffusing element

A measurement system 1 for measuring a distance to an object to be measured comprising a distance calculation unit 14 based on light emitted from a light emitting unit 11 and the light received by a light receiving unit 13; a half mirror 10 and a projection unit 12 such as a lens. An optical path changing unit 16 changes the optical path of the measurement light from the measurement light emitting unit 11 that is reflected by the half mirror so that this reflected light will not be detected by the light-receiving unit 13, therefore reducing noise. The optical path changing unit 16 may be a diffusion lens, a frosted glass or a mirror. The measurement system may be placed in a case 15 where the optical path changing unit 16 is concave and convex portions formed in the surfaces of the inner walls of the case.