An electric supercharging system has an electric supercharger disposed on an intake air passage of an engine and a control unit in which a microcomputer is built. Then, control unit changes an actuation timing of the electric supercharger on the basis of change amounts of a rotational speed and an accelerator opening of the engine. At this time, the control unit changes the actuation timing of the electric supercharger by correcting the actuation timing of the electric supercharger according to the rotational speed of the engine with a coefficient according to the change amount of the accelerator opening.