A fuel cell separator comprising: a reactant gas supply manifold hole penetrating the separator in a thickness direction thereof; a reactant gas discharge manifold hole penetrating the separator in the thickness direction thereof; a groove-shaped spiral first reactant gas channel provided on at least one main surface thereof such that the first reactant gas channel is bent, an upstream end of the first reactant gas channel is connected to the reactant gas supply manifold hole, a downstream end of the first reactant gas channel is connected to the reactant gas discharge manifold hole; and one or more groove-shaped spiral second reactant gas channels provided on at least one main surface thereof such that the second reactant gas channels are bent, at least upstream ends of the second reactant gas channels are connected to the reactant gas supply manifold hole, and the second reactant gas channels run along the first reactant gas channel; wherein the first reactant gas channel includes an upstream portion, a midstream portion and a downstream portion, and the upstream portion and the downstream portion surround the midstream portion when viewed from a thickness direction of the separator, wherein the first reactant gas channel includes a first portion and a second portion located downstream of the first portion, characterized in that the first portion is located closest to the downstream end in the upstream portion of the first reactant gas channel when viewed from the thickness direction of the separator, the second portion is located closest to the upstream end in the downstream portion of the first reactant gas channel when viewed from the thickness direction of the separator, wherein the second reactant gas channel does not exist between the first portion and the downstream end, but exists between the upstream end and the second portion, when viewed in a thickness direction of the separator; and wherein a cross-sectional area of a continuous portion (hereinafter referred to as a first specified portion) of the first reactant gas channel, the continuous portion including at least the first portion and/or a cross-sectional area of a continuous portion (hereinafter referred to as a second specified portion) of the first reactant gas channel, the continuous portion extending from at least the downstream end is/are smaller than a cross-sectional area of at least one second reactant gas channel (hereinafter referred to as a specified second reactant gas channel) of the one or more second reactant gas channels. a reactant gas supply manifold hole penetrating the separator in a thickness direction thereof; a reactant gas discharge manifold hole penetrating the separator in the thickness direction thereof; a groove-shaped spiral first reactant gas channel provided on at least one main surface thereof such that the first reactant gas channel is bent, an upstream end of the first reactant gas channel is connected to the reactant gas supply manifold hole, a downstream end of the first reactant gas channel is connected to the reactant gas discharge manifold hole; and one or more groove-shaped spiral second reactant gas channels provided on at least one main surface thereof such that the second reactant gas channels are bent, at least upstream ends of the second reactant gas channels are connected to the reactant gas supply manifold hole, and the second reactant gas channels run along the first reactant gas channel;