PURPOSE: To provide the efficient diffusion joining method useful for reducing the cost capable of performing satisfactory joining of high quality without using a mold or a retort in the diffusion joining method of large-sized materials to be joined of the complicated shape having the three-dimensional curved surface.

CONSTITUTION: The periphery of the joining face of a skin 1 and a dovetail 2 of a hollow fan blade which are materials to be joined is sealed by TIG welding. However, a sealing part is left to the extent of about 1cm and only the 1cm is welded by EBM, the joining face is vacuum-sealed and then, diffusion joining is performed by hot isostatic pressing(HIP) under HIP conditions of the 910°C HIP temperature, the 1000 atmosphere HIP pressure (Ar gas) and the two hour HIP time. After diffusion joining, the dovetail part is finished by machining work and at this time, a Depo part of welding performed to seal the periphery of the joining face is eliminated.