A numerical control apparatus for machine tool, including: an NC program storage portion; an electronic cam data transformation unit which transforms an NC program into electronic cam data; a constant circumferential velocity control command detection unit which detects whether a command for executing constant circumferential velocity control is present or not in the NC program; a reference axis pitch setting unit which sets the pitch for generating data; a main shaft rotational velocity calculation unit which calculates the rotational velocity of a main shaft on the basis of parameters corresponding to the position of a cutting edge of a tool; an axial feed velocity calculation unit which calculates axial feed velocity on the basis of the calculated rotational velocity of the main shaft; and an axial position data computing unit which calculates axial position on the basis of the axial feed velocity obtained at intervals of the set pitch.