A brushless motor for an electric power tool configured such that a rotor having a bonded magnet is radially disposed on the inner side of a stator having winding wires, wherein (i) the rotor includes a shaft and the bonded magnet that is radially disposed on the outer side of the shaft; or (ii) the rotor includes a shaft, a cylindrical core that is radially disposed on the outer side of the shaft and is made of a material through which magnetic flux easily passes, and the cylindrical bonded magnet that is radially disposed on the outer side of the core, a thickness of the bonded magnet in the radial direction being configured to be larger than that of the core in the radial direction; a through hole into which the shaft, or the shaft and the core are inserted is axially formed at the center of the bonded magnet, a resin is filled between an inner peripheral surface of the through hole and an outer peripheral surface of the shaft or between the inner peripheral surface of the through hole and the outer peripheral surface of the core, an inner wall surface of the through hole of the bonded magnet, and the outer peripheral surface of the shaft or the outer peripheral surface of the core are shaped such that rotation of the shaft or the core with respect to the bonded magnet is prevented through the resin, a plurality of grooves that extend in an axial direction are formed on the inner wall surface of the through hole of the bonded magnet at regular intervals in a circumferential direction, the number of the grooves is configured to be larger than the number of poles of the bonded magnet, a resin block that is formed with the resin is provided on the outside of the shaft in the radial direction such that the rotation of the resin block with regard to the shaft is prevented, and an axial end surface of the resin block has a recess portion and an axial end surface of the bonded magnet has a protrusion that extends in the axial direction and is engaged with the recess portion, or the axial end surface of the resin block has a protrusion that extends in the axial direction and the axial end surface of the bonded magnet has a recess portion that is engaged with the protrusion, such that the axial end surface of the resin block is engaged with the axial end surface of the bonded magnet in a circumferential direction. (i) the rotor includes a shaft and the bonded magnet that is radially disposed on the outer side of the shaft; or (ii) the rotor includes a shaft, a cylindrical core that is radially disposed on the outer side of the shaft and is made of a material through which magnetic flux easily passes, and the cylindrical bonded magnet that is radially disposed on the outer side of the core, a thickness of the bonded magnet in the radial direction being configured to be larger than that of the core in the radial direction; a through hole into which the shaft, or the shaft and the core are inserted is axially formed at the center of the bonded magnet, a resin is filled between an inner peripheral surface of the through hole and an outer peripheral surface of the shaft or between the inner peripheral surface of the through hole and the outer peripheral surface of the core, an inner wall surface of the through hole of the bonded magnet, and the outer peripheral surface of the shaft or the outer peripheral surface of the core are shaped such that rotation of the shaft or the core with respect to the bonded magnet is prevented through the resin, a plurality of grooves that extend in an axial direction are formed on the inner wall surface of the through hole of the bonded magnet at regular intervals in a circumferential direction, the number of the grooves is configured to be larger than the number of poles of the bonded magnet, a resin block that is formed with the resin is provided on the outside of the shaft in the radial direction such that the rotation of the resin block with regard to the shaft is prevented, and an axial end surface of the resin block has a recess portion and an axial end surface of the bonded magnet has a protrusion that extends in the axial direction and is engaged with the recess portion, or the axial end surface of the resin block has a protrusion that extends in the axial direction and the axial end surface of the bonded magnet has a recess portion that is engaged with the protrusion, such that the axial end surface of the resin block is engaged with the axial end surface of the bonded magnet in a circumferential direction.