In a motor, an armature is provided to be opposite to a rotor member for generating a rotating magnetic field. In the armature, plural sets of teeth are arranged in a direction of rotation of the rotor member such that each set of teeth in the plural sets of teeth is within one electrical angular cycle of the rotating magnetic field. The one electrical angular cycle corresponds to one pole-pair pitch of the annular rotor member. A number of teeth in the plurality of teeth within the one pole-pair pitch is set to 2k (k is a natural number), and a number of teeth facing each of the first magnetic poles in the plurality of teeth is set to be equal to or greater than the sum of k and 1.