Abstract: A solid state relay includes a diode for emitting light, a photothyristor circuit responsive to the light from the diode for turning on and outputting a first output signal, the photothyristor circuit having two photothyristors connected to each other in parallel in an opposing direction and a triac circuit responsive to the photothyristor circuit for turning on and outputting a second output signal.

Abstract: A photo coupler device comprises only one layer having a resin material and addition particles provided for molding a pair of a light emitting element and a light receiving element. The addition particles are made of one from silica of crystal form or amorphous form, glass fibre and the like. The addition particles are suspended in the layer in a certain proportion equal to or below about 70% by weight in comparison with the weight of the resin material. A diameter of the addition particles is in the range of about several tens to about one hundred .mu.m. Preferably, the resin material is made of epoxy resin having phenol as a hardener in the case where the light emitting element provides its electroluminescence of infrared region. In another form of the present invention, an additional layer also having another type of resin material and the addition particles can be formed to mold the first layer containing the pair of the elements.