A rotor core is manufactured by forming thin plate-like core pieces including holes, forming a lamination body including insertion holes by laminating the core pieces, and inserting and embedding a permanent magnet in each of the insertion holes of the lamination body. The holes of each core piece include one or more first holes, in each of which a position determining portion for determining the position of the permanent magnet is formed, and one or more second holes, in which a position determining portion is not formed. Each insertion hole of the lamination body is formed by overlapping first holes of some of the core pieces and second holes of the remaining core pieces.