PURPOSE: To obtain an immunodiagnosis system using a galK-HIV chimera antigen capable of detecting a specific disease and a prescribed stage of the disease and examining rapidly, extremely specifically and sharply.

CONSTITUTION: Fusion vector pOTSKF33 comprising a part of galIV antigen brought into contact with the side by a coding sequence of an antigen having uncrossed reactivity to galK and a promoter is obtained from pAlS1 expression vector. The pOTSKF derivative containing galK-HIV antigen fusion is transduced into Escherichia coli AR120 strain to give a gal-HIV chimera antigen. An immunodiagnosis apparatus which comprises a solid carrier, an antibody connected to the solid carrier and the gal-H chimera antigen having a first and a second antigen domains in which the first antigen domain is reacted with the connected antibody and is not subjected to cross reaction with an antibody recognizing the second antigen domain is used to detect the presence of an antibody to head toward a specific antigen.