A tolerance-level display portion 12 is provided in a casing 11 of a head 1 of a photoelectric switch. A light reception signal output from the head 1 is transmitted through a cable 31b of a main body 2. The casing 21 of the main body 2 contains a received light amount display portion 22, a tolerance-level display portion 24, adjust switches 28 and setting switches 29. The CPU in the main body 2 calculates a ratio of a light reception signal to a threshold value to obtain a tolerance level, and applies a control signal corresponding to the obtained tolerance level to a variable power supply circuit. The variable power supply circuit applies a variable voltage, which is dependent on the control signal, through a cable 31a to the head 1. The tolerance-level display portion 12 of the head 1 displays a tolerance level on the basis of the variable voltage by turning on the tolerance-level display LEDs 12a, 12b and 12c.