PURPOSE: To reduce running cost and maintenance cost that are necessary to cool a coolant liquid which is circulatingly used in a cold rolling mill.

CONSTITUTION: The coolant liquid 10 is sprayed from spray headers 3 toward work rolls 1, the coolant liquid which is raised its temp. is received with a mesh internal sheet 12 which is provided in the upper part of an oil pan 4 and the coolant liquid is dispersedly dropped from the mesh-holes 12a of the mesh internal sheet 12. The coolant liquid 10 which is dropped inside the oil pan 4 is cooled by direct heat exchange with the rising flow of gas which is introduced into the inside from an intake port 15 which is provided in the lower part of the oil pan 4.