An electrochemical cell unit according to the present disclosure includes a flat plate type membrane electrode assembly having a structure in which an electrolyte membrane, a first electrode layer disposed on a first surface of the electrolyte membrane, and a second electrode layer disposed on a second surface of the electrolyte membrane are laminated; a first current collector in contact with the first electrode layer of the membrane electrode assembly; an interconnector electrically connected to the first current collector, a second current collector in contact with the second electrode layer of the membrane electrode assembly; and an outer peripheral part made of a metal material that surrounds an outer periphery of the first electrode layer together with the interconnector and the electrolyte membrane to form a gas introduction space for guiding internal gas to the first electrode layer.