PURPOSE: To enable a superconductive magnet for cooling supercritical pressure helium (SHE) to operate stably without increasing the temperature of SHE, by inserting the ends of transfer tubes until they reaches SHE inlet and outlet tubes of the superconductive magnet.

CONSTITUTION: Ends 6c of a forward transfer tube 6a and a return transfer tube 6b are inserted in a forward port pipe 10a and a return port pipe 10b, respectively, with a gap of 0.5 mm or below therebetween, such that the ends 6c reach an SHE inlet tube 17a and an SHE outlet tube 17b, respectively, which are attached to the lower ends of the forward and return port pipes 10a and 10b. Accordingly, the acoustic impedance produced in the space between the transfer tubes 6a, 6b and the port pipes 10a, 10b is mismatched with the acoustic impedance in the SHE inlet and outlet tubes 17a, 17b. Therefore, even if standing acoustic waves are present in the port pipes 10a and 10b, no heat is given to the SHE by the acoustic waves. Thus, the superconductive magnet can operate stably without increasing temperature of the SHE.