A switching power source includes: a transformer; a semiconductor switching element that is provided at a primary side of the transformer; a rectifying-and-smoothing circuit that is provided at a secondary side of the transformer; a switching controller configured to perform a switching control to turn on-and-off the semiconductor switching element, wherein the switching controller comprises: a stoppage circuit configured to perform a stoppage process to stop the switching control when a first-level control signal is input, a restart circuit configured to restart the switching control when a second-level control signal different in its level from the first-level control signal, and a limiting circuit configured to limit, at the time of a start-up of the switching power source, a performance of the stoppage process performed by the stoppage circuit until an output voltage of the switching power source increases to a target voltage.