We developed a ³He cryocooler that can reach down to 0.6 K. It consists of a mechanical refrigerator and a closed-cycle ³He Joule-Thomson expansion circuit. Since the cryocooler uses a mechanical refrigerator for pre-cooling, it does not require cumbersome liquid helium as a cryogen. The developed cryocooler can run for over a month with a simple procedure. We are developing a thermometer calibration apparatus on the basis of the developed cryocooler. The cryocooler can also be applied to other general apparatuses that require low temperature environment.