To attain a minute flow amount adjusting device by connecting a vessel to high and low pressure side pipe passages alternatively and intermittently by means of a valve which is intermittently opened and closed, and flowing fluid of a mean flow rate proportional to intermittent opening/closing frequency of the valve from the high pressure side pipe passage to the low pressure side pipe passage.

A control signal of a control circuit 7 is output to a valve 2. The control signal is adopted to intermittently connect a vessel 1 to a high pressure side pipe passage 3 with an intermittent opening/closing frequency, and connect the vessel 1 to a low pressure side pipe passage 4 with a phase shifted from the high pressure side by a specified rate. The vessel 1 is conected to the high pressure side pipe passage 3 through the valve 2. Gas is flowed from the high pressure side pipe passage 3 to the vessel 1 to equalize the pressure to a value P1. The vessel 1 is then connected to the low pressure side pipe passage 4 to flow a part of the gas inside the vessel 1 to the low pressure side pipe passage 4 into the low pressure side pipe passage 4. The pressure thereinside is lowered to a value P2. The gas of a mean flow rate is fed from the high pressure side pipe passage 3 to the low pressure side pipe passage 4 with one cycle of the opening and closing of the valve 2.