Switching power supply

A switching power supply comprising:

• an insulated transformer including a primary-side coil and a secondary side coil;
• a full-bridge circuit that converts input DC power into AC power and outputs the AC power to the primary-side coil;
• an output circuit that converts AC power input from the secondary-side coil into DC power and outputs the DC power;
• and
• a control circuit that controls the full-bridge circuit by using a phase shift method based on voltage output by the output circuit,
• wherein when a measured value of an amount of phase shift determined from at least one of the voltage and current output by the output circuit is smaller than a theoretical value of the amount of phase shift corresponding to the switching power supply operating in a continuous current mode, the control circuit prolongs dead time used in the full-bridge circuit in accordance with a difference between the measured value and the theoretical value.