Abstract: A hammer tool with a drive motor (16) and a hammer mechanism (35), the hammer mechanism including a drive piston (38) reciprocably movable in a cylinder (34) for driving a hammer piston (39) towards a working tool (13) releasably coupled to the front end of the hammer tool. The hammer tool comprises a changeable motor section (11) containing the drive motor (16) with a motor shaft (19) connected to a first part of a coupling device (50) and a hammer section (12) containing the hammer mechanism (35). The hammer mechanism comprises bevel gears (46, 47) for transmitting drive force from an input drive shaft (45) to the drive piston (38). The input drive shaft is connected to a second part of the coupling device (50) in which a flywheel (48) is incorporated.