A regioselective conjugate of an antibody and a functional substance comprising a structural unit represented by the following Formula (I):






wherein
Ig represents an immunoglobulin unit comprising two heavy chains and two light chains, and is regioselectively bonded to L1 adjacent to Ig via an amino group in side chains of lysine residues in the two heavy chains,
HG represents a hydrophilic group,
RA represents a side chain of a valine residue,
RB represents a side chain of a citrulline residue or the like,
ring A represents a divalent aromatic ring group optionally having a substituent,
R1 and R2 each independently represent a hydrogen atom or a monovalent group,
L1 and L2 each independently represent a divalent
D represents a functional substance, and
r is 1.5 to 2.5, or
a salt thereof, and
substances related thereto,

is excellent in desired properties while controlling a bonding ratio between the antibody and the functional substance within a specific range.