A switching power supply apparatus that includes a pulse generating unit that sets a frequency of a pulse width modulation signal using capacitance applied to a capacitance input terminal, a switching unit that intermittently connects an input voltage, applied from outside the switching power supply, in response to the pulse width modulation signal, an output unit that smoothes the intermittent voltage from the switching unit, and outputs the same, and a capacitance varying unit that varies the capacitance applied to the pulse generating unit in response to a controlling signal. The switching power supply apparatus stabilizes operation of the electronic apparatus by controlling the current increase supplied to the electronic apparatus by receiving in advance the controlling signal for detecting a load increase before the load of the electronic apparatus actually increases.