A robot including a controller and multiple servos, each acting as an actuator, and a supply voltage generator circuit connected to a transmission line between the controller, which controls using the RS485 communication protocol, and the servos. The reference voltage generator circuit maintains one of a pair of differential signals (or an inversion signal) at a constant potential between a high level and a low level. As a result, a TTL communication scheme servo can be mounted and controlled, along with a RS485 scheme servo. A supply voltage generator circuit is formed of a Zener diode and a voltage divider circuit. Without being limited to incorporation at some midpoint on the transmission path, the supply voltage generator circuit can be incorporated in a controller or a hub for splitting a transmission path.