A gas-liquid separator configured to separate and drain water contained in an off-gas discharged from a fuel cell including a cell stack in which a plurality of unit cells is stacked, the gas-liquid separator comprising: an end plate disposable outside the cell stack in a stack direction in which the plurality of unit cells is stacked, the end plate having an end surface located on a side opposite to the cell stack; a gas-liquid separator forming portion that is provided in the end plate, is opened in the end surface of the end plate in the stack direction, and constituting a part of the gas-liquid separator; and a cover member that is disposed to cover an opening of the gas-liquid separator forming portion and constitutes a part of the gas-liquid separator, wherein: the gas-liquid separator forming portion includes a first inner wall portion that serves as a flow path for the off-gas and forms a part of an accumulating portion in which the water separated from the off-gas is accumulated, the first inner wall portion being connected to the opening and having a shape recessed in a thickness direction of the end plate; the gas-liquid separator forming portion includes an inflow port forming portion that forms an inflow port through which the off-gas flows into the gas-liquid separator and a discharge port forming portion that forms a discharge port through which the off-gas is discharged from the gas-liquid separator; characterised in that the cover member includes a second inner wall portion that is connected to an opening provided in a surface of the cover member facing the gas-liquid separator forming portion, and that has a shape recessed in a thickness direction of the cover member, the second inner wall portion being disposed to face the first inner wall portion in the stack direction and forming the accumulating portion together with the first inner wall portion; the cover member includes a drain flow path forming portion that forms a drain flow path through which the water accumulated in the accumulating portion is drained. an end plate disposable outside the cell stack in a stack direction in which the plurality of unit cells is stacked, the end plate having an end surface located on a side opposite to the cell stack; a gas-liquid separator forming portion that is provided in the end plate, is opened in the end surface of the end plate in the stack direction, and constituting a part of the gas-liquid separator; and a cover member that is disposed to cover an opening of the gas-liquid separator forming portion and constitutes a part of the gas-liquid separator, wherein: the gas-liquid separator forming portion includes a first inner wall portion that serves as a flow path for the off-gas and forms a part of an accumulating portion in which the water separated from the off-gas is accumulated, the first inner wall portion being connected to the opening and having a shape recessed in a thickness direction of the end plate; the gas-liquid separator forming portion includes an inflow port forming portion that forms an inflow port through which the off-gas flows into the gas-liquid separator and a discharge port forming portion that forms a discharge port through which the off-gas is discharged from the gas-liquid separator; characterised in that the cover member includes a second inner wall portion that is connected to an opening provided in a surface of the cover member facing the gas-liquid separator forming portion, and that has a shape recessed in a thickness direction of the cover member, the second inner wall portion being disposed to face the first inner wall portion in the stack direction and forming the accumulating portion together with the first inner wall portion; the cover member includes a drain flow path forming portion that forms a drain flow path through which the water accumulated in the accumulating portion is drained. the gas-liquid separator forming portion includes a first inner wall portion that serves as a flow path for the off-gas and forms a part of an accumulating portion in which the water separated from the off-gas is accumulated, the first inner wall portion being connected to the opening and having a shape recessed in a thickness direction of the end plate; the gas-liquid separator forming portion includes an inflow port forming portion that forms an inflow port through which the off-gas flows into the gas-liquid separator and a discharge port forming portion that forms a discharge port through which the off-gas is discharged from the gas-liquid separator; characterised in that the cover member includes a second inner wall portion that is connected to an opening provided in a surface of the cover member facing the gas-liquid separator forming portion, and that has a shape recessed in a thickness direction of the cover member, the second inner wall portion being disposed to face the first inner wall portion in the stack direction and forming the accumulating portion together with the first inner wall portion; the cover member includes a drain flow path forming portion that forms a drain flow path through which the water accumulated in the accumulating portion is drained.