A method of cutting hardened steel using a cBN sintered tool which can improve the surface roughness while maintaining high dimensional accuracy. The upper limit of the tool feed rate is set at such a value that a theoretical surface roughness calculated from the feed rate is between 2/3 and 1/1000 of the target surface roughness. The amount of change of the feed rate between the upper and lower limits of the tool feed rate is set to be between 0.002 and 0.05 mm/rev, and the amount of every feed rate change is set not to be equal to the original feed rate multiplied by an integer. The feed rate is changed forcibly for every number of workpieces for which the total cutting length is between 10 and 1000 meters.