A half bridge step-up switching regulator is configured including an output voltage adjusting switch element Q1 for adjusting an output voltage; a synchronous switch element Q2, connected in series with the output voltage adjusting switch element Q1, that is complementary ON operated when the output voltage adjusting switch element Q1 is turned OFF; a voltage detecting section 10 for detecting the voltage at a connecting node of the switch elements in time of turn-OFF of the synchronous switch element; and a soft switch control section 20 for adjusting the timing of turn-OFF of the synchronous switch element Q2 based on the voltage fluctuation detected by the voltage detecting section 10 to perform zero current switching control.