The disclosed is a deceleration device including a cylindrical brake member fixed to a rotary shaft, a plurality of permanent magnets arrayed in a circumferential direction of a circle around the rotary shaft, a cylindrical magnet holder holding the permanent magnets, and a switching mechanism that switches between a braking state and a non-braking state. The plurality of permanent magnets include primary magnets and secondary magnets that are arrayed alternatively in the circumferential direction. When viewed on a surface facing the brake member, north poles of the primary magnets are circumferentially adjacent to and in contact with north poles of the secondary magnets, and south poles of the primary magnets are circumferentially adjacent to and in contact with south poles of the secondary magnets. The magnetic holder is ferromagnetic.