To enable turning-on/off of constant surface speed control during machining. A numerical control device has a constant surface speed control function for controlling a spindle rotation rate to make a surface speed constant, and includes: a surface speed calculating unit for calculating a surface speed based on a spindle rotation speed having been designated and a distance from a rotation center; a cutting speed setting unit for setting a minimum cutting speed and a maximum cutting speed; a comparison unit for comparing the surface speed with the minimum cutting speed and the maximum cutting speed; and an operation control unit for controlling whether to activate the constant surface speed control function based on a result of the comparison made by the comparison unit.

To enable turning-on/off of constant surface speed control during machining. A numerical control device has a constant surface speed control function for controlling a spindle rotation rate to make a surface speed constant, and includes: a surface speed calculating unit for calculating a surface speed based on a spindle rotation speed having been designated and a distance from a rotation center; a cutting speed setting unit for setting a minimum cutting speed and a maximum cutting speed; a comparison unit for comparing the surface speed with the minimum cutting speed and the maximum cutting speed; and an operation control unit for controlling whether to activate the constant surface speed control function based on a result of the comparison made by the comparison unit.