To provide a rotor for long synchronous motors with a simple manufacturing method by using rotor assemblies for synchronous motors to be formed by laminating and fixing magnetic steel sheets.

A rotor assembly 14 is shrink-fitted to a shaft 16, by fitting a flange protrusion 15 of the shaft 16 into a joining recession 12 of a second end collar 10. After the shrink-fitted assembly 14 is cooled, the next assembly 14 is shrink-fitted by fitting the joining protrusion 9 and the joining recession 12 of first and second end collars 7, 10 to each other. This step is repeated, the rotor assemblies 14 are lapped, and the long rotor of a specified length is manufactured. Consequently, realization of a long rotor becomes feasible and its workability and manufacturability become superior too, since the rotor is manufactured by units of a length with which work is made comparatively easy. In addition, jigs for program arrangement to be used exclusively are not required, since lapping is performed by fitting end collars to magnetic steel plates which are laminated beforehand, using their joining protrusions and recessions.