Abstract: A light emitting and receiving circuit 10 has a light emitting diode 14 with a p-n junction. The light emitting diode 14 is connected with a circuit using the light emitting diode as a light emitting element, and a circuit using the light emitting diode 14 as a light receiving element that measures the intensity of a light. A switching means 16 is connected to the light emitting diode 14, for switching an operating state between a light receiving state where a photoelectromotive force is generated in a direction of biasing the p-n junction when receiving a light and a light emitting state where a forward voltage is applied to the light emitting diode 14 to emit a light according to at least one control signal.