Numerical control unit and nc program creating unit

An NC program creating unit that creates an NC program for a machine tool, comprising:

• a permission information storage unit that stores information on whether changing of an override value is permitted or not for each tool;
• a process determination unit that determines for each machining process in an existing NC program if the machining process is a process using a tool for which changing of the override value is permitted;
• and,
• an NC program editing unit that automatically inserts a start code at a start of the machining process and automatically inserts an end code at an end of the machining process if it is determined by the process determination unit that the machining process is the process using the tool for which changing of the override value is permitted, the start code being a code that allows the override value to be changed, and the end code being a code that no longer allows the override value to be changed.