Tumor antigen peptides derived from cyclophilins or derivatives thereof having the functionally equivalent properties; medicaments, prophylactics, or diagnostics for tumors comprising as an active ingredient such tumor antigen peptides or derivatives thereof, cyclophilins or partial polypeptides thereof, or genes encoding said cyclophilins or partial polypeptides thereof; in vitro use of the above substances for treatment of tumors; and antibodies against the above tumor antigen peptides derived from cyclophilins or derivatives thereof are provided.