An object of the present invention is to solve the problem of occurrences of non-uniform polishing or substrate exposure in a method for polishing a diamond surface of a polished object with a polishing member containing a metal or a metal oxide, and to provide a polishing method which achieves uniform polishing without being affected by a shape of the polished object and by a diamond crystal size. The diamond surface polishing method according to the present invention involves polishing a polished object, the surface of which is made of diamond, by rubbing a polishing member having an elongated shape such as a linear or belt-like shape and containing at least a metal or a metal oxide against the diamond surface, wherein a pressing force of the polishing member is controlled in accordance with material properties of the polishing member and/or a shape of the polished object and a diamond crystal size in a rubbing section so that contact surface pressure in a machining area becomes uniform.