Abstract: An impacting device useful with a pneumatic drive comprises a housing formed with an outer large-diameter bore and an inner small-diameter bore defining an annular shoulder at their juncture. A driving element within the large-diameter bore is limited against movement by the annular shoulder. A plunger movable within both bores is urged by a spring into the large-diameter bore in engagement with the driving element and carries an impacting element, such as a ball, at its opposite end. A air-vent formed through the housing wall is in communication with the first bore at a location so as to be on the inner side of the driving element when the latter is in its initial position, and at the opposite side of the driving element when the latter has been driven by pressurized air pulses to limit against the annular shoulder. Thereafter the plunger continues moving, under its own inertia, to cause the impacting element at the outer end of the plunger to engage the workpiece.