PURPOSE: To eliminate clog of an insulator strip by bringing the strip into pressure contact with an engraving roller to engrave a fold, and forming the strip of a bending unit according to the fold.

CONSTITUTION: An engraving roller 3 is brought into pressure contact with an insulator strip 8, and a fold 29 is engraved on the strip 8 by intermittently feeding a strip feeding unit 4. When the strip 8 is fed to a bending unit 6, a cutting unit 5 cuts the strip 8 at the inlet of the unit 6. The unit 6 bends the strip 8 along a fold 29. A pusher 100 allows the strip 8 to protrude from the unit 6 to the slot 111 of a motor core 109.