Scanner for equalizing torque constant and reducing torque constant variation

A scanner which makes a fluctuation movement in a predetermined range, comprising:

• a rotor formed from permanent magnets having N poles and S poles disposed alternately in a circumferential direction and having a shaft, and
• a stator disposed outside of the rotor and having a casing, a yoke held at the inner circumferential side of the casing, and coils disposed at the inner circumferential side of the yoke;
• wherein each of the permanent magnets forming the N poles and the S poles is configured such that an outer diameter, which is centered about the rotor shaft, of a circumferential intermediate portion of each permanent magnet is smaller than the outer diameter of a circumferential end portion thereof.