A power supply circuit in a PLC includes a first node that receives a DC voltage with a first level, a second node that outputs a voltage for driving a control unit, wiring connecting the first and second nodes, a first rectifier on the wiring having a forward direction from the first node to the second node, a charger for charging and discharging, a first converter that converts a discharging voltage from the charger into a DC voltage with a second level lower than the first level and outputs the voltage, and a second rectifier connected between an output of the first converter and the second node to have a forward direction from the first converter to the second node.