A driving apparatus includes a rotatable rotor with a ring shape, a first
magnetic pole portion, a second magnetic pole portion, and a coil for
magnetically exciting the first magnetic pole portion and the second
magnetic pole portion. The rotor has magnet portions which are divided
along a circumferential direction and differently magnetized. The coil is
disposed radially of the rotor. The condition of -0.333X+0.7>Y is
satisfied where Y is a ratio of a central angle of each first magnetic
pole portion relative to a central angle of each magnetized pole in the
magnet portion, and X is a ratio of an outer circumferential length of
each magnetized pole in the magnet portion relative to a thickness of the
magnet portion in a direction of the rotational axis.
