PURPOSE: To provide an open/close identification sensor, which reduces the degradation of performance to the dirt of a reflection plate and prolongs the service life of performance, concerning the open/close identification sensor to identify the opened/closed state of an opening/closing means such as a shutter or a sliding door, etc.

CONSTITUTION: This sensor is composed of a reflection plate 2 provided with two reflecting planes 2a and 2b having different optical reflection factors, and a detector 3 provided with a light projection part 4 to project light onto the respective reflecting planes 2a and 2b, two of first and second light reception parts 5 and 6 to receive the light reflected on the two reflecting planes, and signal processing part 7 to identify that the opening/closing means is closed when the differential quantity between the quantity of received light respectively at the light reception parts 5 and 6 exceeds a prescribed threshold value.