The diamond film polishing apparatus with hot metals has been presented . Diamond films deposited by both microwave plasma CVD and arc discharge plasma jet CVD are used as workpieces . As a diamond film sways on a polishing plate made of an iron or a nickel heated to 75O''95O C it is finished to flat and glass-like surfaces without any exfoliation. Not only swaying speed but also polishing pressure in this apparatus are extremely low in comparison to a conventional mechanical polishing method. When a cast iron and a molybdenum are used as a polishing plate polishing is not advanced . The polishing rate is highest in a vacuum atmosphere . Among gas atmospheres the rate is highes t in a hydrogen atmosphere . These result show that a diamond film is polished by the diffusion of carbon into a polishing plate. When a diamond film surface is too rough to polish by this apparatus the surface planing with YAG laser is applied then polishing is conducted on the planed surface. 1 .