A separator for a fuel cell includes a contact surface configured to contact a power generating unit of the fuel cell. Groove passages are arranged side by side in the contact surface. Reactant gas flows through the groove passages. At least one of the groove passages includes a wavy section that extends in a wavy shape in planar directions of the contact surface. An upstream portion and a downstream portion in a flow direction of the reactant gas in each groove passage are defined as an upstream portion and a downstream portion, respectively. A wavelength of the wavy section is smaller in the downstream portion than in the upstream portion.