To make surroundings of a material to be treated as a thin oxygen (air) atmosphere by a simple means, and form an oxygen-diffused layer on the surface so as not to form oxides.

This surface treatment method comprises burying a titanium- based material 1 in a powder 3 having oxygen absorptivity, then heating the above titanium-based material 1 together with the powder 3 in an atmospheric air or an oxygen atmosphere at a given temperature for a predetermined time to diffuse and impregnate oxygen atoms into the surface layer of the titanium- based material 1, and to form the oxygen-diffused layer consisting of Ti-0 solid solution on the surface.