The present invention relates to an antibody or a functional fragment thereof that specifically binds to PD-1 with high affinity. Further, a nucleic acid molecule encoding the antibody of the present invention or a functional fragment thereof, an expression vector and a host cell for expressing the antibody of the present invention or a functional fragment thereof, and production of the antibody of the present invention or a functional fragment thereof A method is further provided. The present invention relates to an immunoconjugate and drug composition of the antibody of the present invention or a functional fragment thereof, and a plurality of diseases (cancer, infection and inflammation) using the antibody of the present invention or a functional fragment thereof. Further provided are methods of treating (including sexually transmitted diseases). [Selection figure] None本発明は、高親和力でＰＤ－１と特異的に結合する抗体又はその機能性断片に関する。また、本発明の抗体又はその機能性断片をコードする核酸分子、本発明の抗体又はその機能性断片を発現させるための発現ベクターと宿主細胞、および、本発明の抗体又はその機能性断片の生産方法をさらに提供する。本発明は、本発明の抗体又はその機能性断片の免疫抱合体および薬物組成物、並びに、本発明の抗体又はその機能性断片を使用して複数種の疾患（がん、感染症、および炎症性疾患を含む）を治療する方法をさらに提供する。【選択図】なし
