The present invention provides a switching power supply which reduces power consumption in a standby state and improves power supply efficiency. At the time of starting a standby mode in which the output voltage VFB of the IV converter exceeds a standby detection upper limit voltage from a reference voltage source, the switching operation of the switching element is stopped. This stopping reduces the output voltage VFB of the IV converter along with a power supply voltage VO. When the output voltage VFB is lower than a standby detection lower limit voltage from the reference voltage source, the switching operation of the switching element is resumed.