PROBLEM TO BE SOLVED: To provide a method of screening a microtubule growth inhibitor according to a novel mechanism, and a novel microtubule growth inhibitor.SOLUTION: There are disclosed a method of screening a substance that inhibits the phosphorylation of CLIP-170 by AMPK, wherein the phosphorylation of CLIP-170 by AMPK is employed as an indicator; a method of screening a microtubule growth inhibitor, wherein the phosphorylation of CLIP-170 by AMPK is employed as an indicator; a microtubule growth inhibitor including, as an effective component, the substance that inhibits the phosphorylation of CLIP-170 by AMPK; and a polypeptide of varied-type CLIP-170 wherein an amino acid of CLIP-170 phosphorylatated by AMPK is varied.