A distillation apparatus of the present invention includes: a distillation column group in which a plurality of distillation columns (D1, D2, D3), which are respectively equipped with a reboiler (R1, R2, R3), is connected in the form of a distillation cascade; feed-gas condensers (C'2, C'3) which liquefy feed gases from respective former distillation columns (D1, D2) and feed said liquefied feed gases to respective latter distillation columns (D2, D3); gas-feeding lines (Q A 2, Q A 3) which connect the respective former distillation columns (D1, D2) and the respective feed-gas condensers (C'2, C'3); and liquid-feeding lines (Q G 2, Q G 3) which connect the respective feed-gas condensers (C'2, C'3) and the respective latter distillation columns (D2, D3).