An intake-port core includes a body part having the same outer shape as that of the intake port, a port-injector part having the same outer shape as that of a port-injector insertion part, and an extending part. A cooling-water flow-passage core includes a water-jacket core having the same outer shape as that of a water jacket. The intake-port core is inserted from the extending part thereof into the water-jacket core so as to join the cooling-water flow-passage core to the intake-port core. Thereafter, a core print part that is a separate body from the intake-port core is joined to the intake-port core.