PURPOSE: To control freely the cooling rate of a heated steel material by placing a rotating member between a spray nozzle for cooling the steel material and the steel material and by adjusting the number of rotations of the rotating member.

CONSTITUTION: A steel material 1 heated to a prescribed temp. is put in a receiving section 2 having a through hole 3, and it is cooled with cooling water spayed from a spray nozzle 4 of a large diameter. At this time, a rotating member 7 consisting of two parallel plates 7A, 7A having a prescribed interval G supported by a trunnion shaft 6 is placed between the nozzle 4 and the hole 3. By rotating the member 7 while spraying cooling water from the nozzle 4, the amount of sprayed cooling water reaching the steel material 1 is adjusted to control the cooling rate of the material 1, so the structure can be freely regulated.