A photoelectric switch includes first and second shell halves respectively having first and second coupled surfaces which confront each other along an axis in either a horizontal direction or an upright direction. The coupled surfaces respectively have first and second recessed regions aligned with each other to confine a rolling chamber for a roller to be rollable therein, and define left and right holes at two opposite ends of the rolling chamber, and emitter and receiver accommodating chambers outwardly of the left and right holes for accommodating a light emitter and a light receiver such that a light passage is defined by the left and right holes and the rolling chamber.