PURPOSE: To enable automatic conveyance of fluid, by a method wherein the interior of a bellows part, having the one end in an axial direction connected to a piston, and the other end in an axial direction secured to a cylinder, is filled with a material which phase-changes between liquid and gas due to a fluctuation in the temperature of the interior of the cylinder.

CONSTITUTION: The interior of a bellows part 21 of a driving part 20, having the one end in an axial direction secured to a piston 26 and the other end in an axial direction secured to a cylinder 17, is filled with a material 37 which phase-change between liquid and gas due to fluctuation in the temperature of the interior of the cylinder 17. With the cylinder 17 heated by a heating source 31, fluid 13 at the interior is warmed, and the material 37 at the interior of the driving part 20 is also warmed. Thus, the internal pressure of the driving part 20 is raised by vaporization action of the material 37, the bellows part 21 is expanded, the piston 26 is slid upward, and the heated fluid 13 is fed out through a cylinder output 15. Meanwhile, since during upward movement of a piston, the fluid 13, reduced in temperature a relatively low value through a return pipe, flows in the cylinder 17, the bellows 21 is contracted in contrast with the above. This enables automatic conveyance of the fluid 13.