To provide a main shaft connecting structure for a rotor eliminating any part in a disc part of the rotor from generating excessive stress, eliminating no possibility of loosening of a bolt fastening the disc part to the main shaft, and being superior in reproducibility of the rotor balance in reassembling the rotor in the rotor for a high-speed rotating element such as a molecular pump.

A pan-like recess face 2a concentric to the axial center is provided in one face of a disc part 2 of a rotor 1, a truncated cone projection 2c is projected from the central part of the recess face 2a, the projection part 2c is fitted in a tapered hole 3a in the central part of the front end of a main shaft 3 with interference, and when the disc part 2 and the main shaft 3 are fastened together by using the bolts 4, it is so set that a narrow space part 2a is formed in the internal circumferential side of both annular abutment faces 2b.