The present invention is an invention that aims to provide a technique for designing and evaluating an artificial lung that can comprehensively examine the performance of each element of the oxygenator and that can exhibit comprehensively excellent performance. An oxygenator comprising a gas exchanger part having an external perfusion-type hollow fiber membrane bundle and a heat exchanger part having a heat exchange element, which has gas exchange performance, heat exchange performance coefficient, blood filling amount and blood side pressure loss. Measure and calculate Fp = (Gas exchange performance × Heat exchange performance coefficient) / (Blood filling amount × Blood side pressure loss) to provide an artificial lung whose Fp value is 1.5-2.5.本発明は、人工肺の各要素の性能を統一的に検討でき総合的に優れた性能を発揮できる人工肺を設計し評価する技術を提供することを目的とする発明であり、ガス交換用の外部潅流型中空糸膜束を有するガス交換器部および熱交換用エレメントを有する熱交換器部を備える人工肺であって、ガス交換性能、熱交換性能係数、血液充填量および血液側圧力損失を測定し、Ｆｐ＝（ガス交換性能×熱交換性能係数）／（血液充填量×血液側圧力損失）を計算し、Ｆｐの値が１．５～２．５である人工肺を提供する。
