To provide an optical sensor device having the simple constitution for detecting the light from a light source with constant detecting sensitivity regardless of axial dislocation of the light source.

This optical sensor device has an optical sensor 2 having a prescribed light receiving area and a condensing lens 1 for introducing the light into this optical sensor, and is characterized by keeping light receiving sensitivity of the optical sensor almost constant regardless of the axial dislocation of the light source 3 by arranging the light receiving area of the optical sensor in a position dislocated from a focal position of the condensing lens particularly on the optical axis of the condensing lens.