To discharge liquid inside a container at an optional fixed flow-out speed from a liquid upper surface without using a driving power equipment such as a pump or the like by fixing the height difference of a liquid surface inside the container and a fixed reference point even when a liquid amount inside the container is changed.

In a cylindrical or columnar container 5, the liquid 6 stored in the container 5 is sucked by a suction pipe 10 inserted from the liquid upper surface 7 and discharged to the outside of the container 5 at the optional fixed flow-out speed. In this case, the container 5 is hung by one or plural extension coil springs 9. Then, the spring constant (k) of the extension coil spring 9 is defined as (k)=(maximum weight of liquid 6 stored in container 5)/(maximum liquid depth of container 5) in the case of one spring. Also, in the case of plural springs, (n) is defined as the number of the plural springs and (k)=(maximum weight of liquid 6 stored in container 5)/((n)×(maximum liquid depth of container 5)) is defined. Thus, even when the liquid amount inside the container 5 is changed, the height difference 8 of the liquid upper surface 7 inside the container 5 and the fixed reference point 12 is fixed.