PURPOSE: To execute adjustment at an optional concentration and dispersion degree by collecting an emission at a forward part of a roll stand after finishing of cooling/lubricating performance, individually treating a separated liquid phase and using again as an emulsion.

CONSTITUTION: All the mixture of water/mixture of oil flows into a collecting tank below a roll stand 1, and from here is sent into a collecting and separating vessel 22 through an oil/water mixture conduit pipe 37. A separated oil phase is again settled in an oil collecting vessel 53, and then in succession is subjected to purification of metallic components and additional water separation in an oil purification device 41. A water containing oil phase is returned to the collecting and separating vessel 22 as a mixture phase through an introducing conduit pipe 45 so as to be separated. The purified oil is collected in a pure oil vessel 43, and in some cases fresh oil is added from a fresh oil vessel 44. In the fresh oil vessel 44, emulsifier is mixed to control emulsion. The water phase separated in the collecting and separating vessel 22 is purified by a filter 47, is collected in a pure water vessel 48, and over again is settled.