To provide a rotary drive device for a die, which prevents abnormal wear and breakage of a toothed belt as much as possible and maintains rotational accuracy of a die such as a blanking die.

A rotary drive device 10 for a die has a blanking die 11 for blanking down an iron core piece, which is press-formed into a predetermined shape, from a metallic bar material, and for rotating and laminating the iron core pieces to form a laminated iron core. The rotary drive device 10 for a die has: a driven pulley 13, which is arranged with its shaft core aligned to the blanking die 11; a driving pulley 14, which is connected to the driven pulley 13 via a toothed belt 15 and connected to a power source giving rotating power to the blanking die 11; and a tension mechanism 20, which is provided with a tension pulley 19 coming into contact with a part of the toothed belt 15 and pressing the part. Further, the tension pulley 19 is pressed to the toothed belt 15 via springs 38, 39.

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