Gas/liquid separator

A gas/liquid separator is provided in which separation performance for fluid into gas and liquid is enhanced. A gas/liquid separator includes a body which separates a circulation gas into water and hydrogen gas in a separating space, a supply port from which the circulation gas flows into the inner space, the supply port being provided on the side wall surface forming the separating space, and a discharge port through which the separated hydrogen gas flows out of the separating space, the discharge port being provided on the side wall surface. In this case, the discharge port is provided above the supply port.