To provide a thermal displacement compensation device for a machine tool main spindle allowing high-precision machining at any time regardless of a tool rotation speed.

This device for compensating the thermal displacement of the machine tool main spindle 1 compensates the thermal displacement caused by rotational heat generation of the main spindle 1 of a machine tool. The device has a refrigerant circulation passage 3 circulating a refrigerant cooling the rotating main shaft 1; a temperature detector 5 detecting a temperature of the refrigerant, provided in the refrigerant circulation passage 3 near the main spindle 1; and a control part 7 controlling the machine tool such that the machining starts after the refrigerant temperature detected by the temperature detector 5 reaches a thermal equilibrium temperature.