PURPOSE: To easily prolong the life of a tool for a hot working, such as a plug for rolling a seamless steel pipe to be used under a severe condition like the rolling of a high alloy steel.

CONSTITUTION: In the inclined rolling method for a seamless pipe, plural cooling water spouting-out ports 21 standing opposite each other are provided on a plug surface in plural positions along with a plug moving path in a cooling water bath 13. The quantity of cooling water to be supplied from each cooling water spouting-out port 21, is controlled so that it is gradually and monotonously reduced toward the moving direction of the plug.