A machine tool capable of detecting an ambient temperature change without a detector for detecting the ambient temperature and capable of detecting an abnormality of a temperature detector for detecting the motor temperature. Motor temperature Ti (i=1, 2) and the current feedback Ifi of each motor are read out from the temperature detector for detecting the temperature of each motor of the machine tool. The heating value Qi of each motor is obtained from current feedback Ifi. Motor temperature Ti is calculated and estimated from the heating value Q. Difference Ti between the estimated motor temperature Tmi and the detected temperature Tsi is obtained. When difference between maximum and minimum values of difference Ti exceeds the first threshold value , a temperature detector abnormality is outputted. When it is equal to or less than the first threshold value , the mean value T' of differences is obtained. If the mean value T' is equal to or less than the second threshold value , it is determined that there is no abnormality. If it is equal to or more than the second threshold value , the indication that the ambient temperature has been changed is outputted.