In a controller for a power converter, a switching frequency of a switching element is determined on the basis of at least one of a magnetic parameter of a magnetic component and an electric parameter of the power converter, and the switching frequency changes stepwise in each of M intervals on the basis of one of a predetermined time width and a predetermined electric quantity width, M being an integer not less than 2. A control frequency is a value obtained by dividing the switching frequency by an integer P not less than 2.