A sulfonium salt compound represented by the following general formula (I): where R1 and R2 each denote the same or a different alkyl group having 1 to 18 carbon atoms, R3 and R4 each denote the same or a different alkyl group having 1 to 10 carbon atoms, X− denotes a sulfonate anion or a carboxylate anion, and the substituents denoted by R3O and R4O are each located at an arbitrary position selected from the 2-position to the 8-position of the naphthyl group.