A photoelectric sensor (1, 1A) including a light emitter and a light receiver, the light emitter including a light emitting unit configured to emit a light beam, and a power supply circuit configured to receive supply of electric power through a first power supply line leading to an outside of the light emitter, and supply required electric power to the light emitting unit, the light receiver including a first switching element, connected to a second power supply line leading to an outside of the light receiver, for serving to output a first output signal via a first signal line, a second switching element, connected to the second power supply line, for serving to output a second output signal via a second signal line, and a detection circuit configured to switch a conducting state of each of the first switching element and the second switching element in accordance with an intensity of light detected, wherein the detection circuit is configured to switch the first switching element and the second switching element so as to be brought into conducting states opposite from each other in accordance with the intensity of light detected, the photoelectric sensor further including a third power supply line, such that one end of the third power supply line is, by means of a third switching element, electrically connected to the first power supply line inside the light emitter, and the other end of the third power supply line is electrically connected to the second power supply line outside the light receiver, the light emitter further including the third switching element disposed such that one side of the third switching element is connected to the one end of the third power supply line and the other side of the third switching element is connected to the first power supply line, and a monitoring circuit configured to control a conducting state of the third switching element, and the monitoring circuit being further configured to operate with electric power supplied through the first power supply line and to maintain the third switching element in a conducting state as long as electric power is supplied through the first power supply line. the light emitter including a light emitting unit configured to emit a light beam, and a power supply circuit configured to receive supply of electric power through a first power supply line leading to an outside of the light emitter, and supply required electric power to the light emitting unit, the light receiver including a first switching element, connected to a second power supply line leading to an outside of the light receiver, for serving to output a first output signal via a first signal line, a second switching element, connected to the second power supply line, for serving to output a second output signal via a second signal line, and a detection circuit configured to switch a conducting state of each of the first switching element and the second switching element in accordance with an intensity of light detected, wherein the detection circuit is configured to switch the first switching element and the second switching element so as to be brought into conducting states opposite from each other in accordance with the intensity of light detected, the photoelectric sensor further including a light emitting unit configured to emit a light beam, and a power supply circuit configured to receive supply of electric power through a first power supply line leading to an outside of the light emitter, and supply required electric power to the light emitting unit, the light receiver including receive supply of electric power through a first power supply line leading to an outside of the light emitter, and supply required electric power to the light emitting unit, the light receiver including a first switching element, connected to a second power supply line leading to an outside of the light receiver, for serving to output a first output signal via a first signal line, a second switching element, connected to the second power supply line, for serving to output a second output signal via a second signal line, and a detection circuit configured to switch a conducting state of each of the first switching element and the second switching element in accordance with an intensity of light detected, wherein the detection circuit is configured to switch the first switching element and the second switching element so as to be brought into conducting states opposite from each other in accordance with the intensity of light detected, the photoelectric sensor further including a third power supply line, such that one end of the third power supply line is, by means of a third switching element, electrically connected to the first power supply line inside the light emitter, and the other end of the third power supply line is electrically connected to the second power supply line outside the light receiver, the light emitter further including the third switching element disposed such that one side of the third switching element is connected to the one end of the third power supply line and the other side of the third switching element is connected to the first power supply line, and a monitoring circuit configured to control a conducting state of the third switching element, and the monitoring circuit being further configured to operate with electric power supplied through the first power supply line and to maintain the third switching element in a conducting state as long as electric power is supplied through the first power supply line.