PURPOSE: To provide a suitable brazing filler metal whose base metal is not melted in the case of joining a general iron and steel stock such as Ni-Cr-Mo steel by a liquid phase diffusion joining method, and the joining method using this brazing filler metal.

CONSTITUTION: An iron base brazing filler metal consisting of an iron alloy having a composition containing 4.3-4.0weight% silicon, 3.5-3.0weight% boron, and 2.0-0.5weight% carbon is formed. This iron base brazing filler metal is used as a brazing filler metal, and by heating and pressurizing it under inert gas or a vacuum atmosphere at a temperature of ≤1100°C, liquid phase diffusion joining of an iron and steel stock is executed. Usually, the melting point of the filler metal has a low melting point of 1050-1060°C, therefore, at the time of executing joining of an iron and steel stock by a liquid phase diffusion joining method, a joining temperature can be set to a low temperature area of ≤1100°C sufficient for securing an ideal liquid phase diffusion joining state.