The therapeutic agent for a tumor of the present invention contains Apoptosis Inhibitor of Macrophage (AIM) or a protein variant having substantially the same activity as the AIM as an active ingredient and is substantially free of complement.本発明の腫瘍の治療剤は、Apoptosis Inhibitor of Macrophage(AIM)又は該AIMと実質的に同等の活性を有するタンパク質改変体を有効成分として含有し、補体を実質的に含有しないものである。