A method corrects thermal displacement of a machine tool having a rotational spindle. The method includes detecting a rotation speed of the spindle. A thermal displacement amount of the spindle in the current cycle of execution of a program is estimated by using an arithmetic expression that is based at least on the spindle rotation speed and a thermal displacement amount that has been estimated in the preceding cycle of execution of the program. The estimated thermal displacement amount in the current cycle is used as a correction amount for canceling the thermal displacement of the spindle. Therefore, thermal displacement of a machine tool is corrected with no complicated processes when a spindle rotation speed changes.