PURPOSE: To maintain surely the surface temp. of a billet at a specific point at a target value by detecting the surface temp. of the billet near the outlet of a secondary cooling zone, comparing said temp. with the target temp. at said point and controlling the flow rate of the coolant in the secondary cooling zone according to the deviation.

CONSTITUTION: A surface thermometer 9 is installed near the outlet of a seconddary cooling zone 2 of a curved type continuous casting installation and flow rate control valves V1WVn are installed to supply pipes connected to coolant sprayers provided in respective divided zones S1WSn of the zone 2. The valves V1WVn are connected to respective flowmeters f1Wfn which are connected to a control device 11. The surface temp. of the billet 1 near the outlet of the zone 2 is thus detected by the thermometer 9 and is compared with the target temp. by the device 11. The flow rate of the coolant is controlled according to the deviation via the valves V1WVn by the device 11 while the flow rate is detected with the flowmeters f1Wfn.