Multi-phase interleaving control in a power supply device is accelerated. In addition, in accelerating the multi-phase interleaving control in the power supply device, acceleration in detecting a feedback signal and stabilization of a control system in a high-frequency band are promoted. Eliminating the need of the feedback signal according to a slow response detector, and using a detection signal obtained by a detector for detecting an AC signal capable of rapid response, thereby accelerating the multi-phase interleaving control in the power supply device. Then, the control system is stabilized, by satisfying a condition where gain is equal to 1 or less in a transfer function of the control system including an LC circuit, and a condition where a phase shift caused by dead time of switching time does not affect the sampling cycle.