A normal-time drive cam groove extends from a drive cam specific point, which is defined as a specific point of the drive cam, toward one side in a circumferential direction of the drive cam. A groove bottom at the normal-time drive cam groove is sloped relative to one end surface of the drive cam such that a depth of the groove bottom continuously decreases from the drive cam specific point toward the one side in the circumferential direction of the drive cam. An emergency-time drive cam groove extends from the drive cam specific point toward another side in the circumferential direction of the drive cam.