A single cell of a fuel cell has: a membrane-electrode assembly; and first and second separators holding the membrane-electrode assembly therebetween. The first separator has plural first straight or wavy groove channels that are arranged in parallel to each other in a first in-plane direction. A cross section along the first in-plane direction of each of the plural first groove channels has a first uneven shape. The first uneven shape has a first pitch P1 along the first in-plane direction. The second separator has plural second wavy groove channels that are aligned along the first in-plane direction. A second uneven shape of the plural second groove channels has a second pitch P2 along the first in-plane direction. The first pitch P1 and the second pitch P2 differ from each other, and neither a value of P1/P2 nor a value of P2/P1 is an integer.