To provide a fixing device of a rotor to a shaft allowing easy mounting/demounting of the rotor on/from the shaft having a tapered face.

The fixing device 1 fixes the rotor 6 to the shaft to be mechanically fixed/demounted to/from a mounting portion of the shaft 2 with two sleeves 3, 4. It comprises the shaft 2 having the rotor mounting portion 21 as the tapered face 22 and a spiral portion 23 at the end, an internal sleeve 3 having an inner face as a tapered face 31 to be fitted to the rotor mounting portion 21 of the shaft 2, an external sleeve 4 encircling the outer periphery of the internal sleeve 3 in a locally fitted condition, and a fastening nut 5 threaded to the spiral portion 23 of the shaft 2 for mechanically fixing/demounting the rotor 6 with the rotation of the external sleeve 4 in the direction of pushing or pulling it.