NOVELTY - A stainless steel diffusion bonding product is formed by directly contacting and integrating stainless steel materials by diffusion bonding. Contact interface before joining (pre-contact interface) of cross-section of stainless steel material is observed in perpendicular direction. Penetration of crystal grains is carried out in pre-contact interface in steel material. Grain boundary triple point is formed in position of the other party from pre-contact interface. The number ratio of penetration crystal grain occupying with respect to total crystal grain is 20% or more.    USE - Stainless steel diffusion bonding product for heat exchanger, machine component, fuel cell component, domestic electrical appliances component, chemical plant components, ornament structural component and building materials.    ADVANTAGE - The stainless steel diffusion bonding product has excellent adhesiveness, corrosion resistance and reliability with respect to junction portion.    DETAILED DESCRIPTION - A stainless steel diffusion bonding product is formed by directly contacting and integrating stainless steel materials by diffusion bonding. The contact interface before joining (pre-contact interface) of cross-section of stainless steel material is observed in perpendicular direction. Penetration of crystal grains is carried out in pre-contact interface in steel material by crystal grain boundary movement at the time of diffusion bonding. The grain boundary triple point is formed in position of the other party from the pre-contact interface. The number ratio of penetration crystal grain occupying with respect to total crystal grain contacting the pre-contact interface or the crystal grain over the pre-contact interface is 20% or more, when included angle of the grain boundary in grain-boundary triple point is 150 degrees or less. The length ratio of void-containing location in pre-contact interface position is 5 % or less. An INDEPENDENT CLAIM is included for manufacture of stainless steel diffusion bonding product.