To suppress temperature rise of a working fluid in a tank by an influence of an external heat.

A brine X in a pressure chamber 17 of a pouring cylinder 12 is returned to the side of the tank 27 by reversely driving a reversible pump 29 when a lapse of a fixed time between the finish of one pouring operation and the start of the next pouring operation is timed by a compulsively reversing timer. The reversible pump 29 is stopped when the reverse of the brine X is finished. The brine X in the tank 27 is prevented from vainly being subjected to temperature rise by the influence of the heat in a machine house 5 even if the brine X blocked in a pipeline in the machine house 5 afterwards shows high temperature because the residual amount of the brine X in the tank 27 is considerably increased.