Abstract: A dephlegmator includes a feed gas passage and a refrigerant passage. A feed gas introduced into the feed gas passage from the bottom is heat-exchanged with a refrigerant passing through the refrigerant passage. Components having low boiling points are withdrawn as rectified gases from the top, and components having high boiling points are discharged as condensates from the bottom. The refrigerant passage is divided into a first section on the top side and a second section on the bottom side by a bridgewall. In the first section, a liquid or gas-liquid two-phase refrigerant is introduced from the bottom of the refrigerant passage so as to flow parallel to the feed gas. In the second section, a gas fraction of the refrigerant discharged from the first section flows.