A machine tool controller according to an embodiment of the present invention, for controlling a spindle and a feed axis, includes a motor temperature obtaining unit for obtaining and outputting the winding temperature of a spindle motor as a motor temperature; an inverter temperature obtaining unit for obtaining and outputting the temperature of an inverter that drives the spindle motor as an inverter temperature; a motor temperature comparator for comparing the outputted motor temperature with an overheat temperature for the motor; an inverter temperature comparator for comparing the outputted inverter temperature with an overheat temperature for the inverter; and an overheating assessment unit for imposing a restriction on the output of the spindle motor according to the smaller one of the differences between the motor temperature and the overheat temperature for the motor and between the inverter temperature and the overheat temperature for the inverter.