Disclosed are a photoelectric sensor and a photoelectric sensor system capable of accurately detecting an object without being affected by disturbance even though the object is very thin. A photoelectric sensor according to an embodiment of the invention includes a light emitting unit and a light receiving unit. The photoelectric sensor detects whether there is an object between the light emitting unit and the light receiving unit based on a variation in the intensity of a light signal received by the light receiving unit. The light receiving unit receives a light signal that is emitted from the light emitting unit to the light receiving unit without intersecting the object and a light signal that is emitted from the light emitting unit to the light receiving unit through the object, and is operated in synchronization with a light emission timing signal of the light emitting unit. The intensity of the received light signal that is not attenuated by the object is compared with the intensity of the received light signal that is attenuated by the object to detect information indicating whether there is the object.