PURPOSE: To eliminate a call loss due to a backward leak current, by avoiding the irradiation of the light given from a PNPN element driving light emitting source to the junction to which the backward voltage is applied at the moment of application of said backward voltage.

CONSTITUTION: A light shielding film 36 is used in order to avoid the irradiation of light to a junction J1. As a result, only the junction J1 receives the application of voltage when the voltage is applied backward to an anode A and a cathode K. Thus the film 36 covers only the junction J1 and does not prevent the light to be irradiated to a junction J2. Furthermore the film 36 is made of Al, etc. enlarged to cover completely over a depletion layer region J1S to perform the functions of both an electrode and a light shielding film at one time. In the case of a lateral type, the regions J1 and J2 are irradiated independently of each other. Thus the area of irradiation never reduces for the depletion layer region J2S although the region J1S is completely covered. This does not cause the deterioration of the driving characteristics for a PNPN element.