PURPOSE: To reduce the swelling of an end of a shoe strip connecting pin, to prevent the quenching crack of the pin, and to improve the fatigue strength by blowing a flow of mist on the end of the pin when the pin is hardened.

CONSTITUTION: A heated shoe strip connecting pin 21 is placed on a pair of rolls, an end 22 of the pin 21 is brought into contact with a cylinder 18, and pressure is applied to the pin 21 with a pressing roll while rotating the pin 21. In this state, compressed air is fed to an air flowing hole 12 in a nozzle body 11 to convert water injected from a water injecting hole 15 into mist in a mist forming part 14, and a flow of mist is blown on the end 22 of the pin 21 to cool the end 22, so hardening is carried out. The flow of mist after cooling is exhausted from an exhaust port 23. The extent of swelling of the end 22 of the pin 21 is reduced.