PURPOSE: To attain quick cooling and to shorten the casting cycle by detecting a fact that a die temperature reaches a prescribed temperature and controlling the supply quantity of cooling water, and executing die cooling in accordance with a prescribed cooling speed.

CONSTITUTION: When pouring of a molten metal is started, die temperature rises gradually, and this value is inputted every moment to a controller C through a tempera ture sensor. When its temperature reaches a set temperature, a command is outputted from the controller C and a cooling water supply pump 55 operates, and water feeding to a cooling groove 59 of a die B is started. While operating a data input from a temperature sensor for detecting a temperature fall, an opening of a cooling water quantity regulating valve 57 is controlled under the control of the controller C. When a water cooling temperature reaches a prescribed temperature, water cooling is switched to air cooling, a cooling water opening/closing valve 56 is closed, an air side opening/closing valve 52 is opened, and blast to the cooling groove 59 of the die B is started. As for the blast quantity, an opening of an air flow rate control valve 53 is controlled by the controller, and air cooling is executed to a set air cooling temperature.