The invention enables more efficient CTL induction by applying a transdermal preparation containing a WT1 protein-derived cancer antigen peptide and an ether-type additive, which is liquid at 20° C., to a WT1 protein-derived cancer antigen peptide. The ether-type additive is represented by the formula (1): R1—O—R2 (1), wherein R1 is a hydrocarbon group having 8-24 carbon atoms, and R2 is a group represented by the formula (2):or a group represented by the formula (3): —(CH2CH2O)mH (3), wherein m is an integer of 1-18.