A fuel cell stack comprising a fuel cell module including fuel cells stacked on one another, each fuel cell including a membrane electrode assembly having a power generation portion and two separators (30-30C,40) interposing the membrane electrode assembly, each fuel cell including a gas introduction hole (ML1,ML3) from which power generation gas is introduced, a gas discharge hole (MR1,MR3) from which the power generation gas is discharged, a coolant introduction hole from which a coolant is introduced, and a coolant discharge hole from which the coolant is discharged, the two separators (30-30C,40) in each fuel cell interposing the power generation portion and being provided therebetween with a gas passage communicating with the gas introduction hole (ML1,ML3) and the gas discharge hole (MR1,MR3), each fuel cell including a gas seal portion for preventing the power generation gas from flowing out of the gas introduction hole (ML1,ML3), the gas discharge hole (MR1,MR3), and the gas passage, and a coolant seal portion for preventing the coolant from flowing into a space between the separators (30-30C,40) and the membrane electrode assembly, the fuel cells adjacent to each other in the fuel cell module being provided therebetween with a coolant passage which communicates with the coolant introduction hole and the coolant discharge hole and has a power generation portion cooling portion for cooling the power generation portion;. the gas seal portion including a gas seal projection which projects from at least one of the two separators (30-30C,40) toward the membrane electrode assembly in each fuel cell and is provided with a recess serving as the coolant passage on a side opposite to the membrane electrode assembly, the coolant seal portion including a coolant seal projection which projects from the at least one of the two separators (30-30C,40) toward the membrane electrode assembly in each fuel cell and is provided with a recess serving as the coolant passage on the side opposite to the membrane electrode assembly, at least one of the gas seal projection and the coolant seal projection being provided with a resistance portion for suppressing a flow of the coolant out of the power generation portion cooling portion.-. each fuel cell including a gas introduction hole (ML1,ML3) from which power generation gas is introduced, a gas discharge hole (MR1,MR3) from which the power generation gas is discharged, a coolant introduction hole from which a coolant is introduced, and a coolant discharge hole from which the coolant is discharged, the two separators (30-30C,40) in each fuel cell interposing the power generation portion and being provided therebetween with a gas passage communicating with the gas introduction hole (ML1,ML3) and the gas discharge hole (MR1,MR3), each fuel cell including a gas seal portion for preventing the power generation gas from flowing out of the gas introduction hole (ML1,ML3), the gas discharge hole (MR1,MR3), and the gas passage, and a coolant seal portion for preventing the coolant from flowing into a space between the separators (30-30C,40) and the membrane electrode assembly, the fuel cells adjacent to each other in the fuel cell module being provided therebetween with a coolant passage which communicates with the coolant introduction hole and the coolant discharge hole and has a power generation portion cooling portion for cooling the power generation portion;. the gas seal portion including a gas seal projection which projects from at least one of the two separators (30-30C,40) toward the membrane electrode assembly in each fuel cell and is provided with a recess serving as the coolant passage on a side opposite to the membrane electrode assembly, the coolant seal portion including a coolant seal projection which projects from the at least one of the two separators (30-30C,40) toward the membrane electrode assembly in each fuel cell and is provided with a recess serving as the coolant passage on the side opposite to the membrane electrode assembly, at least one of the gas seal projection and the coolant seal projection being provided with a resistance portion for suppressing a flow of the coolant out of the power generation portion cooling portion.-.