PROBLEM TO BE SOLVED: To provide a surface hardening treatment method which can easily harden the surface of a ferrite-based piece-shaped graphite cast iron material which is extremely reduced in carbon amount in a base organization.SOLUTION: Carbon is diffused in the cast iron material by pressing, rotating and moving a tool to a surface portion of the ferrite-based piece-shaped graphite cast iron material which should be hardened, and after that, a tool passing region is cooled.
