A switching power supply device capable to be connected to an AC power supply via a phase control circuit to cause a load LS, for example a lamp, to operate, the switching power supply device comprising: a rectifying circuit (Rec) configured to receive a phase-controlled alternating voltage from the phase control circuit to rectify to a direct voltage; and a switching operation conversion circuit configured to convert the direct voltage to an output voltage different from the direct voltage, the switching operation conversion circuit including: a switching element being of a normally on type and having a main terminal and a first control terminal, the direct voltage being applied to the switching element, an off driving circuit having at least a second control terminal, the off driving circuit being configured to turn off the switching element by allowing a potential of the main terminal to be higher than a potential of the first control terminal when a current passing through the off driving circuit exceeds a prescribed value, an inductor passing a current at turn-on of the normally on type switching element, and a driving winding configured to control turning on or off the switching element by magnetically coupling with the inductor and supplying an induced voltage to the first control terminal, an end of the driving winding being connected to the inductor, another end of the driving winding being connected to the first control terminal, the off driving circuit being a constant current element, being connected in series to the switching element. a rectifying circuit (Rec) configured to receive a phase-controlled alternating voltage from the phase control circuit to rectify to a direct voltage; and a switching operation conversion circuit configured to convert the direct voltage to an output voltage different from the direct voltage, the switching operation conversion circuit including: a switching element being of a normally on type and having a main terminal and a first control terminal, the direct voltage being applied to the switching element, an off driving circuit having at least a second control terminal, the off driving circuit being configured to turn off the switching element by allowing a potential of the main terminal to be higher than a potential of the first control terminal when a current passing through the off driving circuit exceeds a prescribed value, an inductor passing a current at turn-on of the normally on type switching element, and a driving winding configured to control turning on or off the switching element by magnetically coupling with the inductor and supplying an induced voltage to the first control terminal, an end of the driving winding being connected to the inductor, another end of the driving winding being connected to the first control terminal, the off driving circuit being a constant current element, being connected in series to the switching element. a switching element being of a normally on type and having a main terminal and a first control terminal, the direct voltage being applied to the switching element, an off driving circuit having at least a second control terminal, the off driving circuit being configured to turn off the switching element by allowing a potential of the main terminal to be higher than a potential of the first control terminal when a current passing through the off driving circuit exceeds a prescribed value, an inductor passing a current at turn-on of the normally on type switching element, and a driving winding configured to control turning on or off the switching element by magnetically coupling with the inductor and supplying an induced voltage to the first control terminal, an end of the driving winding being connected to the inductor, another end of the driving winding being connected to the first control terminal, the off driving circuit being a constant current element, being connected in series to the switching element.