PURPOSE: To make it possible to feed fluid without using a specific power device, by exchanging the heat of a heat medium in a closed heat receiving container, alternately with liquid on feeding and the outside air, and by changing the internal volume of an expandable container in accordance with variations in the pressure in the closed heat receiving container.

CONSTITUTION: An expandable container 6 is disposed in a closed heat receiving container 3, having its inside isolated from a heat medium 2 which is charged in the container 3. The inside of the expandable container 6 is communicated with the fluid supply side through a suction passage 4 and a suction control valve 10, and also connected to the fed fluid use side through a discharge passage 5 and a discharge control valve 11. Meanwhile there is provided a radiator 8 for heat-exchange between the heat medium and cooling liquid 14 above the closed heat receiving container 3. The radiator 8 and the inside of the closed heat receiving container 3 are communicated with each other through a heat receiving and radiating control valve 9 which turns on the communication therebetween when the expandable container 6 is at a bottom dead center.