A retroreflective photoelectric sensor has a light-emitting optical system having a light-emitting element and a first polarizer and serving to transmit light from the light-emitting element through the first polarizer, a light-receiving optical system having a second polarizer and a light-receiving element and serving to convert light received through the second polarizer into an electrical signal by the light-receiving element, the first and second polarizers having mutually perpendicular polarizer axes, a single lens for both emitting light from the light-emitting element and receiving light to the light-receiving element therethrough, a beam splitter serving to direct light received from the light-emitting optical system to the single lens and light received from the single lens to the light-receiving optical system, and a phase shifter inserted between the light-emitting optical system and the single lens.