A core of a rotating electrical machine is formed by laminating core plates, which are each formed by a plurality of core pieces. According to the method for manufacturing the core, a belt-like workpiece is first conveyed intermittently in its longitudinal direction. Then, while the workpiece is in a stopped state, side edges of a core piece are punched out. At a downstream position in the conveying direction of the workpiece, the remaining edges of the core piece are cut, so that the core piece is punched out. The punched out core pieces are lined up on a support. The core plate is thus formed, and the core pieces are laminated.