A power supply apparatus capable of setting a ripple current to be not more than an acceptable value regardless of an input voltage is obtained. The apparatus calculates switching frequency by a current detected by a current detector so that the switching frequency is set to be low if the current is large and the switching frequency is set to be high if the current is small. The switching frequency is set to be high if the input voltage is high and switching frequency is set to be low if the input voltage is low depending on a voltage inputted to an input terminal; and a switching element is controlled by restricting the switching frequency so that the switching frequency to be set by the current detected by the current detector is not lower than the switching frequency to be set by the input voltage.