The present inventors discovered that antibodies having weaker antigen-binding activity at the early endosomal pH in comparison with that at the pH of plasma are capable of binding to multiple antigen molecules with a single antibody molecule, have long half-lives in plasma, and have improved durations of time in which they can bind to antigen.本發明提供一種在早期內囊胞內pH的抗原結合活性較在血漿中pH的抗原結合活性弱的抗體,該抗體可以1分子與複數個分子的抗原結合,延長血漿中半衰期,改善可與抗原結合的時間。