To provide a conveyer driving device that reduces component count and thereby delivery time and costs and that improves efficiency and thereby saves energy, is made compact, and has an improved outward appearance.

A conveyer driving device includes a permanent magnet synchronous motor 3 that rotates and drives a driving shaft 2 of a conveyer 1 in a direct-drive method. In a permanent magnet rotor 3d of the permanent magnet synchronous motor 3, low-coercive-force permanent magnets 3p to 3s are arranged, as parts of permanent magnets, that have coercive force of such a level that the amount of magnetization thereof is varied by being energized by an inverter device 11. Windings 3a to 3c of respective phases of the permanent magnet synchronous motor 3 are energized in such a manner that the higher the rotation speed becomes within a predetermined rotation speed range, the more strongly the low-coercive-force permanent magnets 3p to 3s are magnetized and that the lower the rotation speed, the less strongly the low-coercive-force permanent magnets 3p to 3s are magnetized. Thus, the permanent magnet synchronous motor 3 is configured so as to have constant torque within the predetermined rotation speed range.