To obtain an excellent dense joining such that the part between the joined boundary and a metal/alloy to be joined is undistinguishable, by heating a minute element to a prescribed temperature, with a liquid phase made of a part of the base metal and the alloy, and joining the metal by diffusing the liquid phase in the metal maintained in a solid phase.

For example, for the purpose of joining two steel pieces, the surfaces to be joined are coated with Indian ink. Carbon in Indian ink and iron in the steel base metal form an eutectic alloy, whose eutectic temperature is 1,153°C and lower than the melting point of a low carbon steel used and that of iron. Consequently, with the joining boundaries coated with Indian ink, and with a pair of oppositely facing steel pieces heated to a temperature higher than the eutectic temperature, e.g. 1,155°C, the steel pieces will not melt. However, the carbon in contact with the iron on the surface of the steel piece interferes with the crystal lattice of the iron, forming an eutectic alloy of iron and carbon, passing into a liquid phase, rapidly moving and diffusing into the iron crystal in the solid phase of steel.