An object of the present invention is to provide a disk brake having excellent responsiveness. A rotation preventing mechanism 34A prevents a rotation of a carrier 41 (one output member) in a direction causing a piston 12 to return. An internal gear 46 (the other output member) rotates by a predetermined degree to act on the rotation preventing mechanism 34A. When the motor 38 causes a sun gear (input member) to rotate such that the piston 12 moves in a return direction, a rotation of the internal gear 46 according to the rotation of the sun gear 44 releases rotation prevention of the rotation preventing mechanism 34A to the carrier 41. It is possible to release the parking brake without use of a worm gear which is used in the conventional arts for holding a thrust force (self-holding). As a result, it is possible to quickly release the parking brake, and therefore a driver can start to run without delay after parking brake release, whereby the responsiveness is improved.