The present invention provides (1) a self-crosslinking resin (I) having a blocked isocyanate group and a hydroxyl group in the molecule and characterized in that the resin is prepared from a vinyl polymer (A) having at least two free isocyanate groups in the molecule and a polyester resin (B) having at least two hydroxyl groups in the molecule by reacting some of the hydroxyl groups of the resin (B) with some of the free isocyanate groups of the polymer (A), and subsequently reacting a blocking agent with all the remaining free isocyanate groups, and (2) a self-crosslinking resin (II) having a blocked isocyanate group and a hydroxyl group in the molecule and characterized in that the resin is prepared from a vinyl polymer (C) having a free isocyanate group and a blocked isocyanate group in the molecule and the polyester resin (B) having at least two hydroxyl groups in the molecule by reacting some of the hydroxyl groups of the resin (B) with all the free isocyanate groups of the polymer (C).