An electric parking brake system includes an electric motor; a linear motion mechanism that converts the rotational movement of a rotor shaft of the electric motor to a linear movement of a slide member to operate a brake; a locking mechanism that fixes a position of the slide member; a control device that controls the electric motor and the locking mechanism; a brake load estimation unit that estimates a brake force; and an electric parking brake operation instruction device that is arbitrary operable. The control device automatically executes a parking brake operation when a stop state of the vehicle is detected even if the electric parking brake operation instruction device is not operated. The automatically applied parking brake force is set to a value smaller than the normal parking brake force applied by the parking brake operation instruction device.