PURPOSE: To put a small amount of liquid nitrogen into a container with not only supply of inert air but also instantaneous cooling made possible before closing of the container.

CONSTITUTION: A first electrovalve and second electrovalve 7A and 7B grouped in a block 7 and arranged in parallel between a fluid supply conduit 5 and a distribution conduit 6 are provided, and the electrovalves are driven and controlled from the outside of the block by first and second micrometric adjustment screws 9A and 9B. When one of the electrovalves is in operation to deliver successively identical quantities of fluid, the other electrovalve is adjusted, based on a new value corresponding to changeover of the electrovalves. A third electrovalve 7C for blowing gas under pressure to expel the remaining drops in the distribution conduit is connected to the block 7.