A machining condition generation method for a numerically controlled machine tool which can conduct machining under a suitable machining condition without changing an initial machining program even when the change of a work material becomes necessary after the preparation of the machining program has been completed. This method comprises the steps of dividing a function for determining the machining condition such as a spindle rotating speed and a feed speed of a tool into a first function portion which does not depend on a work material and a second function portion which depends on the work material, storing only the first function portion as reference values of the machining condition in a storage medium along with a machining program when the machining program is prepared, setting the second function portion by designating a work material to the numerical controller at the execution stage of the machining program (a2), and combining the first function portion and the second function portion to generate machining conditions (a9 and a11).