A synchronous rectification type forward converter enables safe and reliable synchronous control of each switching element without requiring complicated control, and realizes higher efficiency. SOLUTION: First and second delay circuits which respectively input PWM signals and turn on / off control of a main switching element and a rectifying switching element after a predetermined same delay time elapse, a predetermined reference potential, a PWM signal and a choke coil The operational amplifier circuit receives a potential and turns on and off the commutating switching element, and the operational amplifier circuit is a commutating switching element when the PWM signal is off and the choke coil potential tends to fall below the reference potential. Operates to keep the choke coil potential at the same potential as the reference potential while turning on the commutation switching element from on when the PWM signal is on or when the choke coil potential exceeds the reference potential. . [Selected figure] Figure 1
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