A switching power supply device includes: a positive voltage output circuit connected to a direct-current power supply, the positive voltage output circuit including a first switching element, a voltage boosting inductor, a first rectifying element and a first capacitor; a negative voltage output circuit connected to the power supply, the negative voltage output circuit including a second switching element, a voltage dropping inductor, a second rectifying element and a second capacitor; and an adder circuit configured to add switching currents flowing when the first and the second switching elements are operated. The circuit elements of the positive voltage output circuit are symmetrical with those of the negative voltage output circuit. The first switching current of the positive voltage output circuit and the second switching current of the negative voltage output circuit are generated in mutually opposite directions and are inputted to the adder circuit.