A gate voltage control device includes a detection circuit, a plurality of isolation transformers including primary coils and secondary coils, a primary circuit connected to the primary coils, secondary circuits connected to the secondary coils, and voltage regulator circuits connected to the secondary circuits and gates. The detection circuit transmits signal corresponding to detected physical quantity to the primary circuit. The primary circuit cyclically performs applying a variable voltage in a waveform that corresponds to the signal transmitted from the detection circuit between both ends of each primary coil. Each secondary circuit converts the variable voltage generated in the corresponding secondary coil to a direct voltage. Each voltage regulator circuit is powered by the direct voltage converted by the corresponding secondary circuit as a power source, and changes a change-pattern of the corresponding gate voltage according to a waveform of the variable voltage generated in the corresponding secondary coil.