To provide a method for quenching a cylinder from the outside so that the quenched depth can be changed according to the longitudinal position after the cylinder is quenched one time.

The method for quenching the outer surface of the cylinder by arranging an induction heating coil 2 and a water-spouting device 3 around the cylinder 1, and quenching the cylinder while moving them comprises: inserting a metal rod 5 into the cylinder 1 from at least one end of it while controlling the length of the inserted metal rod 5 to be the half or less of the whole length of the cylinder 1; and allowing the metal rod 5 to contact with the inner surface of the cylinder in at least one part in a longitudinal span of the cylinder. Further the quantity of heat per unit length of the cylinder can also be changed by changing one or both of a heating power and moving speeds of the induction heating coil 2 and the water-spouting device 3 according to the longitudinal position of the cylinder.