Tpo modified antibody agonist.

A modified antibody comprising two or more V regions of H chain and two or more V regions of the L chain of an antibody and showing agonist action TPO crossreactivity with TPO receptor, wherein the modified antibody is : (i) a multimer of single chain Fv comprising a V region of H chain and a V region of L chain; or (ii) a single chain polypeptide comprising two or more V regions of the H chain and two or more chain regions L.