A hammer drill, such as a petrol hammer drill, is provided with a rotatable hammer pipe supported in a shell. The hammer pipe can be rotationally driven by a transmission gear arranged on the hammer pipe through a transmission device. An impact mechanism arranged in the hammer pipe. The impact mechanism has a piston which can be driven into reciprocating stroke motion, and a work type change-over switch for work types of "impact drilling" and "chisel drilling". The work type change-over switch has a manually operable change-over knob and a change-over mechanism connected to the change-over knob. The change-over mechanism couples the hammer tube with the transmission gear in the set position "impact drilling" of the change-over knob and non - rotatable fixes the hammer tube in the shell in the set position "chisel drilling".

Characteristic of a hammer drill (such as a petrol hammer drill): the conversion mechanism is provided with a switch ring which can be fixed on the hammer tube without relative rotation and axially movable, and the switch ring is equipped with at least one radially protruding locking lug on the outer side facing away from the hammer tube, and the locking lug is configured to be inserted into at least one axial groove fixed on the transmission gear in a circumferential direction in a form-fitting manner on the one hand and into an axial tooth part fixed with the shell in a circumferential direction in a form-fitting manner on the other hand.