A hammer drill comprising: a housing; a final output shaft rotatably supported in the housing and adapted to have a bit attached thereto; a rotation mechanism disposed in the housing and configured to transmit torque to a gear which is rotatably provided on the final output shaft; an impact mechanism disposed in the housing and configured to strike the bit; and a torque limiter provided on the final output shaft and configured such that when a torque applied to the final output shaft does not exceed a setting torque, a rotation of the gear is constrained so as to allow the torque to be transmitted to the final output shaft, whereas when the torque applied to the final output shaft exceeds the setting torque, the gear slips to thereby uncouple the torque transmission to the final output shaft, wherein the torque limiter comprises: a cam ring adjacent to the gear, and configured to be provided on the final output shaft so as to be unitarily rotatable with the final output shaft and to have cam projections on a surface facing to the gear; rolling elements received in corresponding through-holes formed in the gear at positions concentrically with the cam projections, and engageable with the cam projections in their rotational directions, and urging means configured to urge the rolling elements toward the cam ring so that when the torque does not exceed the setting torque, the rolling elements are engaged with the cam projections, wherein when the torque exceeds the setting torque, the rolling elements pass the cam projections within the through-holes against the urging means and roll on the cam ring, so that the gear slips on the cam ring to thereby uncouple the torque transmission to the cam ring, characterized in that the rolling elements are rollers and an axis of each roller lies in conformity with a radial direction of the gear. a housing; a final output shaft rotatably supported in the housing and adapted to have a bit attached thereto; a rotation mechanism disposed in the housing and configured to transmit torque to a gear which is rotatably provided on the final output shaft; an impact mechanism disposed in the housing and configured to strike the bit; and a torque limiter provided on the final output shaft and configured such that when a torque applied to the final output shaft does not exceed a setting torque, a rotation of the gear is constrained so as to allow the torque to be transmitted to the final output shaft, whereas when the torque applied to the final output shaft exceeds the setting torque, the gear slips to thereby uncouple the torque transmission to the final output shaft, wherein the torque limiter comprises: a cam ring adjacent to the gear, and configured to be provided on the final output shaft so as to be unitarily rotatable with the final output shaft and to have cam projections on a surface facing to the gear; rolling elements received in corresponding through-holes formed in the gear at positions concentrically with the cam projections, and engageable with the cam projections in their rotational directions, and urging means configured to urge the rolling elements toward the cam ring so that when the torque does not exceed the setting torque, the rolling elements are engaged with the cam projections, wherein when the torque exceeds the setting torque, the rolling elements pass the cam projections within the through-holes against the urging means and roll on the cam ring, so that the gear slips on the cam ring to thereby uncouple the torque transmission to the cam ring, characterized in that the rolling elements are rollers and an axis of each roller lies in conformity with a radial direction of the gear. a cam ring adjacent to the gear, and configured to be provided on the final output shaft so as to be unitarily rotatable with the final output shaft and to have cam projections on a surface facing to the gear; rolling elements received in corresponding through-holes formed in the gear at positions concentrically with the cam projections, and engageable with the cam projections in their rotational directions, and urging means configured to urge the rolling elements toward the cam ring so that when the torque does not exceed the setting torque, the rolling elements are engaged with the cam projections, wherein when the torque exceeds the setting torque, the rolling elements pass the cam projections within the through-holes against the urging means and roll on the cam ring, so that the gear slips on the cam ring to thereby uncouple the torque transmission to the cam ring, characterized in that the rolling elements are rollers and an axis of each roller lies in conformity with a radial direction of the gear.