To provide a gas/liquid separator for a fuel cell which exerts a stable gas/liquid separation function without receiving the effect of the ambient temperature.

The gas/liquid separator includes an inlet port of a water-containing offgas discharged from a fuel cell that generates power on feeding a reaction gas, a body which separates the water-containing offgas into water content and a gas, a drain pipe which drains the separated water content, and a discharge pipe which discharges the separated gas. The body has a heat insulating structure.