PURPOSE: To smoothly supplement liquid helium by providing a bypass tube for an emergency valve of an exhaust tube from a liquid helium tank, and mounting an operation valve in the bypass tube.

CONSTITUTION: Even if the pressure in a tank rises when supplying liquid helium 8, helium gas is exhausted through a piping system such as an exhaust tube 7, a bypass tube 13 and an exhaust duct 9 having pressure loss lower than a cooling tube 6 having larger pressure loss by opening the operation valve 14 of the tube 13. Accordingly, the pressure rise in a liquid helium tank 1 is suppressed, and sufficient pressure difference can be obtained to a liquid helium supply source 1. Thus, the supplying speed of the liquid helium to the tank can be sufficiently obtained.