An electrically powered brake system capable of performing a self-diagnosis of elements of the electrically brake system to diagnose a failure before a vehicle is driven is provided. The electrically powered brake system having a parking brake having a conversion mechanism 6 converting a rotary motion of a motor 2 into a linear motion, propelling a piston 7 according to the rotation of a rotor 2A of the motor 2 by the conversion mechanism, pressing brake pads 3 and 4 against a disc rotor 5 by the piston to generate a braking force, and retaining the braking force by a locking mechanism 10 has a control unit 20 performing a diagnosis of elements constituting the system during actuation of the parking brake. The control unit performs a diagnosis of a fail safe relay 26 receiving the supply of electric power of the motor, and performs diagnoses of a braking force sensor 8, a rotation angle detecting sensor 9 and a current sensor.