An apparatus for optically detecting an object position includes: position detection light sources irradiating light onto the object; a light guide plate receiving the light and emitting it onto a detection area to form an intensity distribution in the detection area; a light detector having light receiving portions receiving the light reflected by the object; and a signal processing portion detecting the object position based on the intensity distribution, wherein light incident portions receiving the light and side portions except for the light incident portions are provided on outer periphery side portions of the light guide plate, a light emission surface emitting the light incident from the light incident portions toward the detection area is provided on a plane portion of the light guide plate, and at least a portion of the side portions is an anti-reflection surface.