High machining accuracy is required for precision components of optical, aircraft and other various parts. In precision machining, thermal deformation of machine tool is one of main cause that deteriorates the machining accuracies. Accordingly, controlling temperature of the spindle and other components of the machine tool is significantly important to achieve desired machining accuracy. In general, forced fluid cooling is used for removing generated heat in the machine tool. It is desired to change appropriately the cooling conditions for the target component such as spindle according to heat generation that depends on the various machining conditions. However, conventional chiller for machine tools does not have appropriate temperature control resolution and response. In this paper, we propose a new method of fluid temperature control that achieves precise temperature control and better responsiveness. In this proposed method, temperature of cooling fluid is controlled by mixing cooling fluids that are different temperatures. Then, we develop temperature control system for machine tools depend on this method. Control performances of this system are evaluated experimentally and theoretically. Finally, further to improve control performance of this system, we investigate effectiveness of disturbance observer incorporated into this system.