Punching structures each include a die, a punch that cooperates with the die to stamp a workpiece, a die supporting member that applies lateral pressure to core pieces stamped out from the workpiece, and a counter pressure applying mechanism that applies counter pressure toward the punch to the core pieces from the side opposite to the punch. The punching structures also include selecting mechanisms, respectively. The punching structures laminate core pieces while applying lateral pressure and counter pressure to the core pieces. The punching structures are arranged along the conveyance direction of the workpiece. The selecting mechanisms select one of the punching structures to be put in a pause state, so that one of the punching structures is put in a pause state during a stamping operation of the punching structures.