The present invention relates to a hybrid type onium salt having an iodonium salt and a sulfonium salt in the molecule, Useful, for example, as a cationic type photopolymerization initiator and an acid generator for a chemically amplified resist and provides a hybrid type onium salt shown by the general formula [1]: and R4 is an alkyl group, an alkenyl group, an aryl group or an aralkyl group, which may have a substituent selected from the group consisting of a halogen atom, an alkyl group, a haloalkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group and an amino group which may be substituted or a group shown by the general formula [2]: and a polymerization initiator or an acid generator, comprising said onium salt.