The first control device is connected to a power supply. The second control device is connected to the first control device via a power supply line and operates with power supplied from the first control device via the power supply line. The switch switches whether or not to make the power supply and the power supply line conductive to each other. The power supply unit is configured to supply power to a power supply line. When the switch is in the conduction state, power is supplied from the power supply to the power line at a first voltage. When the switch is in a non-conductive state, power is supplied from the power supply unit to the power supply line at a second voltage. The first controller switches a switch to transmit the pulse signal to the second control device via a power supply line.