PURPOSE: To make stable mass production of a uniform thin strip possible by controlling the temp. of the cooling water to be supplied into a cooling roll in accordance with the deviation of the actually measured value of the surface temp. of the roll from a set value.

CONSTITUTION: A quick cooling roll 8 is revolved at a high speed, and molten metal is quickly cooled thereon to solidify to a thin strip 9. Cooling water is conducted from a rotary joint 13 through a hollow shaft 14 in the inside cylinder 12 of the roll to the part under the roll surface and is discharged through a hollow shaft 15 and a rotary joint 16. The discharged water is once stored in a water storage tank 17. Part thereof is sucked into a pump 21 for the purpose of recirculation and part thereof is discharged through an overflow pipe 18. The surface temp. of the roll is measured with a thermometer 19, and the signal thereof is fed to a controller 20, where the signal is compared with a set value and is allowed to cascade to a water temp. controller 22 so as to maintain the set value at all times. The signal of the thermometer 23 and the set signal of the controller 20 are collated, and the openin of a valve 24 connecting to a high pressure cooling water pipe 25 is regulated so as to attain the set value, whereby the prescirbed water temp, is obtained. On the other hand, the signal of a flow rate detector 26 enters a flow rate controller 27, where the signal is compared with a set value, and a valve 28, is controlled, whereby a constant flowrate is maintained at all times.