To provide a cam-driven hammer mechanism for a power tool.

The cam-driven hammer mechanism 14 has a drive mechanism housing 46 connectable to the housing of a power tool, a first cam member 102, a second cam member 104, and a gear assembly 54 for connecting the first and second cam members on a driving basis to a driveshaft 42 so that they can rotate in opposite directions. The first and second cam members each have at least one cam surface 106, 122, which is oriented at a steep angle to the axis of the tool element and is complementary to and engageable with the other cam surface. The second cam member has an impact surface engaging the tool element to give it an impact. When the cam members are rotated in opposite directions, the cam surfaces engage each other and the second cam member is moved in one axial direction relative to the first cam member. As the counterrotating state of the cam members is continued, the cam surfaces disengage from each other and the second cam member is moved in the opposite axial direction relative to the first cam member to thus give an impact to the tool element.