An electrically insulated type of switching element drive circuit supplies an AC voltage via a transformer to a control electrode drive circuit that controls a switching element, with the frequency or amplitude of the AC voltage being modulated in accordance with required on/off operation of the switching element, and with the output AC voltage from the transformer being rectified to obtain a DC supply voltage that is continuously supplied to the control electrode drive circuit. The control electrode drive circuit detects a condition of the AC voltage and controls the switching element accordingly.