An electric power system includes: a switching power supply converting an AC into a DC and operating in an on mode and an off mode; a power supply control unit activated when electric power is supplied from the AC power supply, and the power supply control unit being configured to control an oscillation operation of the switching power supply according to the mode designation signal; a mode control unit generating the mode designation signal; and an auxiliary power supply configured to supply electric power to the mode control unit when the switching power supply does not oscillate. In one of the on mode and off mode, the mode control unit performs outputs a consecutive-pulse signal to the power supply control unit. In the other mode, the mode control unit performs a restriction process of restricting output of the consecutive-pulse signal.