A valve timing controller includes a driving circuit, a control circuit, and a signal line. Receiving electric power from a power source, the drive circuit drives an electric motor according to the control signal, and outputs the rotative direction signal showing the rotation direction of the electric motor. A controlling circuit outputs the control signal generated according to the rotation-direction signal. A signal line transmits the rotation-direction signal to the controlling circuit from the drive circuit. The drive circuit outputs a high-level signal showing the normal rotation direction, and a low level signal showing the reverse rotation direction of the electric motor. When a power supply voltage falls below to the acceptable value, the drive circuit maintains the voltage level of the signal line at high level.