Fuel cell stack

A fuel cell stack, comprising single cells stacked in a first direction, wherein

• each single cell includes:
• a power generating unit;
• and
• a first separator and a second separator that hold the power generating unit between the first separator and the second separator,
• the first separator and the second separator each include:
• a facing surface that faces the power generating unit;
• and
• an opposite surface that is located on a side opposite to the facing surface, the opposite surface of the first separator and the opposite surface of the second separator are each provided with groove passages that extend in a second direction, a cooling medium flowing through the groove passages,
• the first separator of each single cell includes first protrusions that protrude toward the second separator of another single cell that is adjacent in the first direction, the first protrusions being in contact with the second separator,
• the groove passages include groove passages that are located at outermost positions in a third direction, the third direction intersecting with both of the first direction and the second direction,
• the first protrusions are provided on an outer side of at least one of the groove passages that are located at the outermost positions in the third direction, the first protrusions being arranged side by side in the second direction,
• each of the first protrusions includes a top wall portion and two side wall portions located on opposite sides of the top wall portion in the second direction, and
• at least one of the two side wall portions includes a step portion having a shape of a step in the first direction.