A decelerating apparatus includes a brake member, primary and secondary permanent magnets and pole pieces. The primary permanent magnets are arranged in a circumferential direction to face an inner or outer peripheral surface of the brake member with a gap in between. Each of the primary permanent magnets has two opposite magnetic poles arranged in a radial direction. The secondary permanent magnets and the pole pieces are placed in the gap and arranged in the circumferential direction. Each of the secondary permanent magnets has two opposite magnetic poles arranged in the circumferential direction. Each of the pole pieces is positioned between adjacent secondary permanent magnets. Magnetic pole arrangements of adjacent primary permanent magnets are opposite to each other. Magnetic pole arrangements of adjacent secondary permanent magnets are opposite to each other. Each of the secondary permanent magnets has a trapezoidal cross-sectional shape including an upper base and a lower base.