Novel proteins which have cell death inducing activity or proliferation inhibitory activity on cancer cells; fragments of such proteins; genes coding such proteins; monoclonal antibodies to such proteins; reagents which induce apoptosis on cells including cancer cells in vitro for investigation of the mechanism of cell death induction, and which are obtained from the proteins including the amino acid sequence of SEQ ID No. 1 of the sequence listing, fragments thereof, genes coding these; and carcinostatic agents.