In a polymer electrolyte membrane fuel cell, a groove (cathode-side gas flow path) in a cathode-side separator, and a groove (anode-side gas flow path) in an anode-side separator are formed such that air and hydrogen flow in a direction opposite to the direction of gravity. A surface treatment may applied to the surface of the grooves such that the hydrophilicity is higher on the downstream side than on the upstream side in the grooves.