An electrochemical reaction cell stack including a plurality of unit cells and flat plate-shaped electrically conductive members arranged in a first direction. The electrically conductive members include: a first member having a first surface including a first flat portion and a protruding portion and a second member both located on the first side of the first member in the first direction, the second member having a second surface facing the first surface and including a second flat portion and a recessed portion facing the protruding portion. The thickness of the second member is larger than the thickness of the first member in the first direction. The depth of the recessed portion of the second member from the second flat portion is larger than the protruding length of the protruding portion of the first member from the first flat portion in the first direction.