Disclosed is a part program execution method for converting a part program, which has been created in an automatic programming language, into NC data in a format capable of being executed by an NC unit. When an error present in a part program is detected during execution of the part program (PPM), an inquiry (M2) inquiring as to whether the part program is to be corrected is displayed on a display screen (CRT) together with an error message (M1). If implementation of a correction is designated, a correction screen is displayed and the part program is re-executed from the beginning thereof in response to designation of the end of the correction.