a power hammer drill includes a tool holder and an air cushion striking mechanism for driving a tool and including a striker , a reciprocating piston for displacing the striker , and an axially displaceable guide tube for guiding the piston . a device for holding the striker in a forward position thereof adjacent to the tool holder in an idling condition of the hammer drill is provided in the hammer drill . the device has a guide element fixed in the drill housing for guiding the guide tube . the guide tube has a control opening for venting the air cushion and which remains in open or closed condition dependent on axial position of the guide tube .