A gas channel forming plate (22, 32) for a single cell of a fuel cell, the gas channel forming plate (22, 32) being suitable to be arranged between a membrane electrode assembly and a plate-shaped separator base (21, 31) and comprising: a plurality of groove-shaped gas channels (25, 35) arranged at intervals on a surface that faces the membrane electrode assembly; a groove-shaped water channel (26, 36) formed on a back side of a protrusion (23, 33) located between an adjacent pair of the gas channels (25, 35); a plurality of pairs of communication passages (27, 37) arranged at intervals in a direction orthogonal to a direction in which the gas channels (25, 35) extend and formed in the inner protrusions (23, 33); a plurality of pairs of ribs (271, 371) arranged at equal intervals in the direction in which the gas channels (25, 35) extend and comprised in each inner protrusion (23, 33), the plurality of pairs of ribs (271, 371) extending in the direction orthogonal to the direction in which the gas channels (25, 35) extend and protruding into the water channels (26,36), and thereby allowing the plurality of communication passages (27, 37) to connect the gas channels (25,35) and the water channels (26, 36) to each other; and a plurality of guide portions (28, 38) formed by causing an inner wall surface of each gas channel (25, 35) to protrude inward in the gas channel (25, 35) such that a cross-sectional area of the gas channel (25, 35) is partially narrowed, the gas channel forming plate being characterized in that the guide portions (28, 38) are formed such that an edge (273, 373) of each communication passage (27, 37) on an upstream side in a flowing direction of gas flowing in the gas channel (25, 35) is arranged in a range in which, in a velocity vector of the gas, a directional component directed from a side corresponding to the membrane electrode assembly toward the separator base (21, 31) has a positive value; each guide portion (28, 38) includes an inclined surface (281, 381) in which a protruding amount of the inner wall surface of the gas channel (25, 35) increases toward a downstream side in the flowing direction; and the gas channel forming plate (22, 32) is a plate of which a cross-sectional shape in the direction orthogonal to the direction in which the gas channels (25, 35) extend has projections and depressions. a plurality of groove-shaped gas channels (25, 35) arranged at intervals on a surface that faces the membrane electrode assembly; a groove-shaped water channel (26, 36) formed on a back side of a protrusion (23, 33) located between an adjacent pair of the gas channels (25, 35); a plurality of pairs of communication passages (27, 37) arranged at intervals in a direction orthogonal to a direction in which the gas channels (25, 35) extend and formed in the inner protrusions (23, 33); a plurality of pairs of ribs (271, 371) arranged at equal intervals in the direction in which the gas channels (25, 35) extend and comprised in each inner protrusion (23, 33), the plurality of pairs of ribs (271, 371) extending in the direction orthogonal to the direction in which the gas channels (25, 35) extend and protruding into the water channels (26,36), and thereby allowing the plurality of communication passages (27, 37) to connect the gas channels (25,35) and the water channels (26, 36) to each other; and a plurality of guide portions (28, 38) formed by causing an inner wall surface of each gas channel (25, 35) to protrude inward in the gas channel (25, 35) such that a cross-sectional area of the gas channel (25, 35) is partially narrowed, the gas channel forming plate being characterized in that the guide portions (28, 38) are formed such that an edge (273, 373) of each communication passage (27, 37) on an upstream side in a flowing direction of gas flowing in the gas channel (25, 35) is arranged in a range in which, in a velocity vector of the gas, a directional component directed from a side corresponding to the membrane electrode assembly toward the separator base (21, 31) has a positive value; each guide portion (28, 38) includes an inclined surface (281, 381) in which a protruding amount of the inner wall surface of the gas channel (25, 35) increases toward a downstream side in the flowing direction; and the gas channel forming plate (22, 32) is a plate of which a cross-sectional shape in the direction orthogonal to the direction in which the gas channels (25, 35) extend has projections and depressions.