Abstract: This pneumatic machine tool includes a driving shaft (14) driven in rotation by pneumatic drive means (12), a driven tool-carrier shaft (16), a gear mechanism (18) disposed between the driving shaft and the driven shaft to drive the latter, a set of sensors (22) for measuring operating parameters of the machine tool, and a central control unit (20) in which are stored algorithms for controlling machining as a function of data received from the sensors, the gear mechanism including means (24, 26, 28, 30) for changing the gear ratio. The gear mechanism includes primary and secondary sets (24, 26) of toothed wheels with different demultiplication ratios, each adapted to rotate freely relative to the driving shaft (14). The speed changing means include a positive clutch (28) constrained to rotate with the driving shaft (14) and axially mobile relative thereto between two end positions in which the positive clutch (28) is engaged with respective sets of toothed wheels (24, 26).