To eliminate the rising-up of cooling liquid to a heating conducting body side even in the case of increasing the flow rate of the cooling liquid more than that of the conventional device.

In a cooling jacket 200A for spouting the cooling liquid to a part heated with an induction heating coil 100 arranged below the induction heating coil 100 for induction-heating while shifting a groove part WA in the inner surface of a cup part W as a cylindrical work, a slit 240A opened on a surface facing the heated part and directing diagonally downward and desirably having ≥3 mm slit width and a static pressure plate 233A for straightening the supplied cooling liquid in the interval till reaching the slit 240A, are arranged, and the tube diameter from the static pressure plate 233A to the slit 240A is made almost constant.