Abstract: Electric resistance heating means is embedded in a forging tool so that the temperature thereof may be maintained at a desired forging temperature. Therefore the present invention makes it possible to forge light metal alloy workpieces such as aluminum workpieces which have been hitherto considered to be difficult to be forged by rotary forging machines. In addition, better quality of forgings as well as considerable improvement of productivity may be ensured. Thus, reduction of labor and material in a forging process can be attained.