In the present invention, a catalyst composition comprising the following amine compounds of (A) and (B) and/or (C) is used and further, a raw material-blended composition further containing a polyol component and water is used. (A) A quaternary ammonium salt represented by the following general formula (1): wherein each of R1 to R3 represents a hydrocarbon group having 1 to 12 carbon atoms, R4 represents an alkyl group or an aromatic hydrocarbon group having 1 to 18 carbon atoms, and X represents an organic acid group having an acid dissociation constant (pKa) of 4.8 or less; (B) A hydrophobic amine compound; (C) A heterocyclic tertiary amine compound.