A safety PLC having duplex power supply circuits, includes: a first output-stage transistor; a first DC power supply that drives the first output-stage transistor; a second output-stage transistor; a second DC power supply that drives the second output-stage transistor; a signal transfer path that includes a resistor and connect the first output-stage transistor to the second output-stage transistor; and a pair of overvoltage protection units, each of which is disposed between a pair of output terminals of the corresponding one of the first and second DC power supplies and restricts the maximum value of an output potential difference between the pair of output terminals.