<p>A gas-dissolving device is provided with a gas discharge valve which has a gas inlet in a bottom portion of the gas discharge valve and is provided at a top portion of a gas-liquid separation vessel, vent ports which are formed in the gas inlet and introduce a part of gasses accumulated in the top portion of the gas-liquid separation vessel into an interior of the gas discharge valve, and a wall portion which is formed at an outside of the vent ports and suppresses a liquid flow into an interior of the gas inlet.</p>
