Abstract: The invention is intended to develop a drug capable of directly or indirectly inhibiting the activation of caspase. Specifically, the invention provides a caspase 3 inhibitor comprising a protein comprising the same or substantially the same amino acid sequence as that represented by SEQ ID NO: 1, 2, 3 or 31 or a salt thereof. The protein of the invention, a partial peptide or a salt thereof is useful as a pharmaceutical such as a prophylactic and/or therapeutic agent for AIDS, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, pigmentary retinopathy, cerebellar degeneration, myelodysplastic syndrome, aplastic anemia, sideroblastic anemia, myocardial ischemia, conduction disturbance, chronic cardiac failure, graft-versus-host disease, or congenital or acquired enzymatic defect.