Synchronous motor having component identical to that of another kind of synchronous motor and method of manufacturing synchronous motors

A synchronous motor is driven by three phase alternate current. The rotor core includes a laminated body configured by laminating plate members made of electrical steel sheet. Each plate member is formed in a substantially circular shape in a plan view and formed with projections along an outer circumference thereof. The number of slots of the stator is 3xy when variable x is a natural number and variable y is a positive odd number. The number of poles of the rotor is (3y+1)x or (3y−1)x. The number of projections of each plate member is a common measure of (3y+1)x and (3y−1)x. The laminated body has a structure in which the plate members are laminated so that the projections are shifted relative to one another.