To provide a curable resin composition, particularly photocurable and thermosetting resin composition, rapidly advancing curing reaction at a relatively low temperature and capable of forming a cured film excellent in many properties without causing heat fogging, discoloring of the cured film and curing shrinkage, and to provide a printed circuit board in which an insulating layer between a solder resist and/or a conductor circuit layer is formed by the cured material.

The curable resin composition comprises (A) a carboxy group- containing resin, (B) a compound having an oxetanyl group and (C) an organophosphonium salt compound having the structural formula (1) [wherein R1, R2, R3 and R4 are each a 2-20C alkyl group, a hydroxyalkyl group, an aryl group or aralkyl group and they may be mutually same or different and X represents a weakly nucleophilic anion species]. The photocurable and thermosetting resin composition comprises further (D) a photopolymerizable monomer and (E) a photopolymerization initiator in addition to the components (A) to (C).