An opposed (through beam) arrangement consists of a receiver located within the line-of-sight of the transmitter. In this mode, an object is detected when the light beam is blocked from getting to the receiver from the transmitter. A retroreflective arrangement places the transmitter and receiver at the same location and uses a reflector to bounce the light beam back from the transmitter to the receiver. An object is sensed when the beam is interrupted and fails to reach the receiver. A proximity-sensing (diffused) arrangement is one in which the transmitted radiation must reflect off of the object in order to reach the receiver. In this mode, an object is detected when the receiver sees the transmitted source rather than when it fails to see it. Some photoeyes have two different operational types, light operate and dark operate. Light operate photoeyes become operational when the receiver "receives" the transmitter signal. Dark operate photoeyes become operational when the receiver "does not receive" the transmitter signal. A photoelectric sensor comprises a light collecting block having a reflective mirror formed on an inner surface of a light transmitting window and a concave mirror including a light passing portion, whereby the reflective mirror is opposed to the concave mirror. Further, the photoelectric sensor comprises an electronic circuit block having a photoelectric element, a plurality of electronic components and a wiring substrate, wherein the photoelectric element is positioned on a light collecting point of the light collecting block.