An electric disk brake that prevents uneven abrasion of a disk rotor when the brake is not in operation. Rotation of an electric motor is slowed down by a differential speed reducing mechanism, and is converted to linear motion of a piston by a ball ramp mechanism. When the brake is not in operation, the piston is retracted by reverse rotation of the electric motor so that a predetermined pad clearance is maintained. When the brake is not in operation, a pad-retracting-control electric current is supplied to the electric motor so that the piston is biased backward while being maintained in one position. When the brake is not in operation, contact of the disk rotor with the brake pads due to runout of the disk rotor triggers smooth retracting of the piston, thereby preventing uneven abrasion of the disk rotor.