Numerical control device

A numerical control device (1) of a machine tool capable of controlling its spindle rotating speed includes: a program analyzing unit (2) that reads ahead a machining program (6) by one block or more and analyzes a command for the machine tool; and a command determining unit (3) that determines, based on a result analyzed by the program analyzing unit (2), whether a command posterior to a spindle control command causes any machining problem when the command is executed during a spindle rotating speed change, outputs a first command, in which some problem occurs in the machining, after the spindle rotating speed reaches the commanded rotating speed, and output a second command, which is other than the first command, before the spindle rotating speed reaches the commanded rotating speed.