To provide a switching power device which operates stably at the on/off operation of an output on/off switch, even when a capacitive load is connected to its output terminal, does not have a superfluous power loss, has a high quality, and excellent in productivity.

This switching power device is provided with a transformer T1, a rectifying circuit D3, C3 which rectifies and smoothes the secondary-side output of the transformer T1, a switching element Q2 which is connected in series to a DC output line rectified and smoothed by the rectifying circuit D3, C3 and opens or closes that line, a control circuit Q3 which controls on/off of the switching element Q2 on the basis of a control signal ENB from outside, and a buffer circuit C5, D5, R8 which is connected between the switching element Q2 and the control circuit Q3 and lightens the change of an output current caused by on/off operation of the switching element Q2.