A power supply device comprising: rectification means that converts AC power input from an AC power supply into DC power and supplies the DC power to a load; an inductive element connected in series between an AC power supply input terminal and the rectification means; switching means that is connected in parallel between paths of an AC voltage applied via the inductive element to the rectification means, and performs opening and closing operations; smoothing means (14,14a) connected to a DC terminal side of the rectification means in parallel with the rectification means; zero cross detection means for detecting a zero cross point of a waveform of an AC voltage output from the AC power supply; and control means that controls the opening and closing operations of the switching means, wherein the control means compares a predetermined reference waveform signal with a reference level (Vth1,Vth2) to generate a drive pulse signal in order to cause the switching means to perform a plurality of opening and closing operations at predetermined cycles, the drive pulse signal has a long pulse with a long opening time of the switching means, and a short pulse (P2,P3,P4) with a shorter opening time than the long pulse, the long pulse is generated by comparing the reference waveform signal with a first reference level, and the short pulse (P2,P3,P4) is generated by comparing the reference waveform signal with a second reference level different from the first reference level. characterised in that the long pulse is generated by comparing a trapezoidal wave (S11a) contained in the reference waveform signal with the first reference level, and the short pulse (P2,P3,P4) is generated by comparing a triangular wave (S11b,S11c,S11d) contained in the reference waveform signal with the second reference level different from the first reference level. rectification means that converts AC power input from an AC power supply into DC power and supplies the DC power to a load; an inductive element connected in series between an AC power supply input terminal and the rectification means; switching means that is connected in parallel between paths of an AC voltage applied via the inductive element to the rectification means, and performs opening and closing operations; smoothing means (14,14a) connected to a DC terminal side of the rectification means in parallel with the rectification means; zero cross detection means for detecting a zero cross point of a waveform of an AC voltage output from the AC power supply; and control means that controls the opening and closing operations of the switching means, wherein the control means compares a predetermined reference waveform signal with a reference level (Vth1,Vth2) to generate a drive pulse signal in order to cause the switching means to perform a plurality of opening and closing operations at predetermined cycles, the drive pulse signal has a long pulse with a long opening time of the switching means, and a short pulse (P2,P3,P4) with a shorter opening time than the long pulse, the long pulse is generated by comparing the reference waveform signal with a first reference level, and the short pulse (P2,P3,P4) is generated by comparing the reference waveform signal with a second reference level different from the first reference level. characterised in that the long pulse is generated by comparing a trapezoidal wave (S11a) contained in the reference waveform signal with the first reference level, and the short pulse (P2,P3,P4) is generated by comparing a triangular wave (S11b,S11c,S11d) contained in the reference waveform signal with the second reference level different from the first reference level.