The mechanism of curving that occurs during the quenching process of Japanese swords has not been clearly explained. Experiments on this phenomenon were conducted using Japanese sword type specimens made of the same steel and through the same processes as Japanese swords, and model Japanese sword type specimens made of carbon steel (S55C) and austenitic stainless steel (SUS304) by machining. Applying the simulated strains-based approach to heat treatment simulation results for these expexperiments, it was found that positive plastic strain and transformation strain on the cutting-edge side are the main contributors to curving generation in Japanese sword.