PURPOSE: To obtain a low-priced insert with excellent durability, by using low-priced heat resisting steel as a material while padding a heat resisting alloy of excellent heat resistance and oxidation resistance to be welded to an acutely angular part in a jet hole and forming a part except the acutely angular part by cold forging and simple machining.

CONSTITUTION: An insert main unit 1, when a Diesel engine is in operation, provides temperature distribution in which only an acutely angular part of a jet hole 2 is heated to 800°C or more with the other part in a low temperature. Consequently, a cheap material of heat resisting steel, which performs press work by a cemented carbide die and upper and lower cemented carbide metal molds changing a shape of the die and the metal molds one after another, prepares recesses, corresponding to thickness, lateral width and longitudinal width of heat resisting alloy layers 5, 6, in the peripheral edge acutely angular part of the jet hole simultaneously forms insert internal and external diametric parts. After the heat resisting alloy layers 5, 6 are welded padding said recess by gas welding or the like, the jet hole 2 is finished by machining. In this way, the insert main unit 1, cheap and rich in durability, is obtained by the simplified manufacturing method.