Included are a switching power supply device main body, and a frequency control circuit that controls the switching frequency of a switching element in accordance with a feedback signal in accordance with the output voltage of the switching power supply device main body. The frequency control circuit is divided into a frequency control region wherein the amount of the feedback signal is greater than a predetermined boundary value and a frequency control region wherein the amount is less, linear frequency control whereby the switching frequency of the switching element is caused to change linearly in accordance with the feedback signal is executed in the frequency control region wherein the feedback amount is less, and linear cycle control whereby the switching cycle of the switching element is caused to change linearly in accordance with the feedback signal is executed in the frequency control region wherein the feedback amount is greater.