PURPOSE: To control the transfer of a fluid to a fluid receiving container from fluid supplying source container based on the detected phase of the fluid by detecting whether the fluid is in a gaseous phase or liquid phase at a prescribed height in the receiving container.

CONSTITUTION: Whether a fluid is in a gaseous phase or liquid phase at a prescribed position 14 in a receiving container 2 is detected by reducing the pressure of a sample fluid taken from the fluid through a capillary tube 39 and measuring the temperature of the pressure-reduced sample fluid in a thermostat chamber 40. The temperature of the fluid after pressure reduction is compared with that of the fluid before pressure reduction by means of a comparator 42 and whether the fluid was a gas or liquid before the pressure reduction is judged in accordance with the temperature of the fluid after pressure reduction, whether the temperature is substantially equal to or lower than the temperature before pressure reduction. The transfer of the fluid to the container 2 from a fluid supplying source container 1 is controlled based on the phase of the fluid judged at the position 14.