Provided is a gas dissolving device capable of dissolving gas in a liquid in a supersaturated state and maintaining such a saturated state in a stable manner, and being easily attached to a water server or the like.The gas dissolving device generates hydrogen water by dissolving hydrogen in water, and discharges the hydrogen water from an outlet. The gas dissolving device includes a dissolving chamber that stores under pressure generated hydrogen water introduced therein, and pressure reduction and transfer means for preventing pressure variation in a tube-shaped passage that connects the dissolving tank and the outlet due to an action of discharging the hydrogen water from the outlet, and for forming a laminar flow.