Abstract: A hammer machine comprises a machine housing (10) with a cylinder (11) in which a reciprocating drive piston (40) via a gas cushion (44) drives a hammer piston (15) to impact on respectively to move away from a tool (20) carried by the housing (10). The movement of the hammer piston (15) away from the tool (20) is supported by underpressure in the gas cushion (44) and rebound. A connecting passage (52) in the drive piston (40), the cylinder (11) or the hammer piston (15) comprises a one-way valve (57) and a throttling means (53) via which the gas cushion (44) is replenished by ambient air for regulating the gas cushion pressure during operation of the drive piston. The one-way valve (57) closes to prevent escape of gas from the gas cushion (44). A damping cylinder (51) in communication with the connecting passage (52) can be provided on one of the pistons (40;15), which, when the piston tend to collide, sealingly cooperates with a damping pistons (50) on the other piston (15;40) so as to prevent collision.