A semiconductor relay device (1) includes a signal input unit (2) for inputting an alternating current signal for relay driving purpose, a direct current insulation member (3) for blocking a direct current electricity of the alternating current signal, a voltage multiplying circuit (5) for multiplying the signal voltage, after the direct current electricity has been blocked, by an integer number, and a relay circuit (4) including two metal-oxide semiconductor field-effect transistors (6, 7) having respective sources connected with each other and connected in a reverse series with each other and also having respective gates connected with each other. Those metal-oxide semiconductor field-effect transistors (6, 7) are caused to undergo a bidirectional ON-Off operation when the respective gates of those metal-oxide semiconductor field-effect transistors (6, 7) are brought into a conducting state by a signal of which voltage has been multiplied by the voltage multiplying circuit (5).