Numerical control unit and nc program creating unit

A numerical control unit is provided that can change an override value according to various workpiece materials and can extend the tool life. A numerical control unit (10) includes a variation storage unit (11) that stores a variation in override value of a feed speed or a spindle speed for each workpiece material, an override value setting unit (13b) that sets the override value based on the variation (ΔRv) in override value according to the material of a workpiece being machined; and a control unit (13c) that changes the feed speed or the spindle speed based on the override value.