Disclosed is a method for screening an immune modulator. More specifically, disclosed is a method of screening an immune modulator, an anticancer agent and an agent for treating autoimmune diseases, which regulate the cell surface expression level of gp96, using the binding of the region of amino acids 54-192 of AIMP1 to the region of amino acids 699-799 of AIMP1, set forth in SEQ ID NO: 18. Also disclosed is a method of diagnosing autoimmune diseases using the binding.