A gas separation composite membrane, containing: a gas-permeable supporting layer; and a gas separating layer containing a crosslinked polyimide resin, over the gas-permeable supporting layer, in which the crosslinked polyimide resin is composed of a polyimide compound having been crosslinked through an ester linking group, in which the polyimide compound contains a repeating unit of formula (I), a repeating unit of formula (II-a) or (II-b), and a repeating unit of formula (III-a) or (III-b), and in which a ratio [κ] of a site forming a crosslinked chain mediated by the ester linking group to an imide group (the number of specific crosslinkable sites/the number of imide groups) is more than 0.4 and less than 0.5.