PURPOSE: To dispense with use of an expensive edge tool, form a continuous flame spraying layer, and heighten the close contact strength by carrying out broach work on grooves before cementation quenching is carried out, carrying out grinding work on the conical friction surfaces and back faces from which cementation is prevented, and lastly carrying out flame spraying of flame spraying metal such as molybdenum.

CONSTITUTION: Before cementation quenching is carried out, on the whole circumference of the friction surfaces 22, broach work is carried out on grooves 23 in parallel with the rotation axis of a synchronizer ring 21 in succession to machine work of the conical friction surfaces 22. Thereby, use of a cemented carbide tool can be dispensed with, and the device life of an edge tool is lengthened, and productivity is also improved. After the broach work and the cementation quenching are carried out, flame spraying of tungsten or the like is carried out, and since a continuous flame spraying coating film 27 is formed on the whole surfaces of the grooves 23 and projections 24, close contact strength of this flame spraying layer 27 is heightened, and durability is improved.