To provide a temperature measuring device for a thermal displacement compensation device, in which the values output by temperature sensors are shared among a plurality of machine tools, and thus the total number of the temperature sensors is reduced, thereby suppressing the total cost and also reducing the failure risk of the temperature sensors installed in the machine tools. A plurality of machine tools are made to use, in order to monitor a temperature of each of one or more common positions set in advance, temperature information measured by a temperature sensor installed at any position in the common positions in each of the machine tools, as temperature information of any position in the common positions without a temperature sensor installed in another machine tool in the plurality of machine tools.