In a switching power supply circuit of the invention, a low-voltage node capacitor is connected between a primary-side low-voltage stable potential node and a secondary-side low-voltage stable potential node, and a high-voltage node capacitor is connected between a primary-side high-voltage stable potential node and an anode of a rectifier element. Thereby, it is possible to provide the switching power supply circuit which achieves, with a simple configuration, both of noise reduction and potential stabilization of stable potential nodes.