A numerical control device for controlling a machine tool automatically selects the tool of the specified kind from among a plurality of tools of the same kind disposed in the magazine locations or holders. The numerical control device includes registers for storing the kinds and the lives of the tools disposed in respective magazine locations. Thus, when a tool select command specifying a tool kind is inputted, the magazine location in which the tool of the specified kind having a remaining life is selected by studying the contents of the registers in sequential order. The device further includes registers for storing adjustment values of the tools in the magazine locations, and thus can automatically effect the adjustment operation of the newly selected tool. Preferably, the device includes a tool damage detector and automatically changes the tool in use when it is damaged or reaches the end of its life in the middle of the machining operation.