The switching power supply is provided with a voltage converter including a switching element for inputting a voltage from an input terminal, and has a spread spectrum function of varying a switching frequency in the switching element within a predetermined variation range. The switching power supply has a frequency setting unit that sets the variation range of the switching frequency and raises a lower limit value of the set variation range when a value of the voltage input from the input terminal is equal to or more than a predetermined threshold, and a signal generator that generates a control signal for driving the switching element by varying the switching frequency within the variation range set by the frequency setting unit.