A gas/liquid separator in which separation performance for fluid into gas and liquid is enhanced is provided.
A gas/liquid separator 10 includes a body 40 which separates a circulation gas into water and hydrogen gas in a separating space S1, a supply port 45 from which the circulation gas flows into the inner space S1, the supply port 45 being provided on the side wall surface 43 forming the separating space S1, and a discharge port 48 through which the separated hydrogen gas flows out of the separating space S1, the discharge port 48 being provided on the side wall surface 43. In this case, the discharge port 48 is provided above the supply port 45.