Provided is a method for maintaining cutting quality in which a work surface can be reliably maintained at a predetermined hardness or less regardless of a disturbance during cutting. The method includes a data-acquiring step of acquiring, as a target cutting resistance, the cutting resistance of a machining tool (7) during cutting performed such that the hardness of a surface layer is lower than a predetermined hardness by adjusting machining conditions; and a cutting step of performing cutting while detecting the cutting resistance of the machining tool (7) during cutting and performing control such that the detected cutting resistance is lower than the target cutting resistance.