A power supply system includes: a switching power supply configured to rectify and smooth an AC voltage of an AC power supply to generate a predetermined DC voltage; a low-capacity power supply circuit that generates a zero-cross detection signal corresponding to zero-cross points of the AC power supply based on a rectified current flowing in a smoothing capacitor; and a controller configured to receive the zero-cross detection signal from the signal generating circuit and perform a determining process of determining whether it is possible to perform detection process of the zero-cross points based on a voltage value of the zero-cross detection signal. If the control unit determines that it is possible to perform the detection process of the zero-cross points, the control unit performs a zero-cross point detecting process of detecting the zero-cross points based on the zero-cross detection signal.