In a method for brazing a sheet material without use of flux, an inert gas is firstly introduced into an oxygen pump to reduce an oxygen partial pressure in the inert gas to 1×10−10 Pa or less, and the sheet material is heated in a brazing furnace in an atmosphere of the inert gas discharged from the oxygen pump. A core alloy of the sheet material or a brazing filler alloy cladded to a surface of the core alloy contains Mg. Both the core alloy and the brazing filler alloy may contain Mg. Accordingly, brazability of the sheet material is sufficiently improved.