A carboxyl resin according to the present invention is obtained by a process including following steps: epoxy groups on a resin (a) having two or more epoxy groups in one molecule is made to react with 0.3-0.85 mol of a monocarboxylic acid (b) per one epoxy-group equivalent weight to obtain a reaction product (c); the epoxy group or groups on the reaction product (c) are made to react with 0.15-0.95 mol of a polybasic acid (d) per one epoxy-group equivalent weight to obtain a reaction product (e); and the epoxy group or groups on the reaction product (e) are further made to react with 1.0-5.0 mol of a monocarboxylic acid (f) per one epoxy-group equivalent weight. The carboxyl resin thus obtained has an acid value within a range from 20 to 200 mgKOH/g and is soluble in an organic solvent.