Abstract: A pressure intensifier is automatically driven repeatedly by compressed air from a compressed air source to produce highly compressed air for storage in a pressure chamber. The pressure chamber is selectively connected to or disconnected from a drive cylinder having housed therein a drive piston, under the control of a valve mechanism provided therebetween. By the actuation of the valve mechanism the highly compressed air stored in the pressure chamber is introduced into the drive cylinder to propel the drive piston, driving a nail or like fastening element into a hard receiving material such as concrete.