ELECTRIC PARKING BRAKE DEVICE

According to an electric parking brake system, a power loss of when detecting a position or a displacement of a plunger is reduced without arranging a sensor, and a mounting space is also reduced. A resonance capacitor (54) is connected to a coil (37) of a solenoid (9) to form a resonance circuit, and a drive current superimposed with a resonance frequency is input to the solenoid (9) forming the resonance circuit. When the position of the plunger (10) in the coil (37) is changed, the inductance of the coil (37) changes and the resonance frequency moves. The position or the displacement of the plunger (10) is detected from such change without arranging the senor, and thus an installation space is not necessary. Therefore, the change in the detection value (change in resonance point) of both ends of the solenoid (9) is detected by superimposing the oscillation output in such manner, whereby a large power is not required and the loss is also small.