PURPOSE: To reduce cost by eliminating the need for a magnet for index and an index sensor and to facilitate manufacture by eliminating the position adjustment of the index sensor.

CONSTITUTION: In the title brushless motor with a rotor case 35 retaining a magnet 6 inside, a stator core 19 with a coil 9 opposing the magnet 6. Hall elements 18U, 18V, 18W for detecting the magnetic field of the magnet 6, and a drive circuit for transmitting drive current to the coil 9 based on the output signal of the Hall elements 18U, 18V, and 18W, one part 6a of the magnet 6 is exposed from the opening side of the rotor case 35. At the same time, a magnetic flux increase/decrease means 35a is formed at one part of the peripheral wall of the rotor case 35, the Hall elements 18U, 18V, and 18W are laid out outside In the radial direction from the peripheral wall of the rotor case 35, and an index signal processing circuit for synthesizing index signals by input the output signals of the Hall elements 18W (18U and 18V) is provided.