To provide a small-sized and lightweight motor for a robot which has desirable inertia and is useful for a robot.

The motor for a robot has a stator 27 around which a coil 37 is formed. The stator 27 is fixed to a first member 21. A motor shaft 24 is supported rotatably by the stator 27 and connected with a second member 22. A permanent magnet 44 is disposed on an inner peripheral surface of an outer rotor 43 fixed to the motor shaft 24. The outer rotor 43 is accommodated in a recessed part 45 formed in the first member 21. The stator 27 and the first member 21 constitute wholly closed structure for accommodating the outer rotor 43.