In a power generation unit of a fuel cell stack, bosses of a first metal separator and bosses of a second metal separator are provided to sandwich a first membrane electrode assembly at first sandwiching positions on both sides of the first membrane electrode assembly, oppositely to each other in a stacking direction. Bosses of a second metal separator and bosses of a third metal separator are provided to sandwich a second membrane electrode assembly at second sandwiching positions on both sides of the second membrane electrode assembly, oppositely to each other in the stacking direction. Bosses of the first metal separator and bosses of the third metal separator protrude toward a coolant flow field, and contact each other at positions offset from the first and second sandwiching positions.