To provide a high frequency-induction hardening apparatus with which objective material can efficiently be cooled with a little volume of cooling liquid by improving the holes for discharging the cooling liquid, such as cooling water.

A cooling device 2 is provided with a jacket 8 which is relatively shiftable to the steel tube 7 for supporting a plurality of nozzles 11 on the surface faced to a steel tube 7, and a water-supplying device 9 for supplying the cooling water into the plurality of nozzles 11. Each of the plurality of nozzles 11 is formed by setting a spiral-shaped member in the inner part of an outer-coating tube. At the tip-end part of the outer-coating tube, an outlet hole of cooling water is arranged, and at the other-end of the outer-coating tube, an inlet hole of cooling water is arranged, and the diameter of the outlet hole is made to be smaller than the outer diameter of the spiral-shaped member. The cooling water supplied into the jacket 8 with the water supplying device 9, is entered into the inner part of the nozzle 11, and after giving a spiral-movement with the spiral-shaped member, the cooling water is spread and discharged as the drill-state from the outlet hole of the nozzle 11 and hit to the steel tube 7 to cool the steel tube 7.

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