Polymerization initiator composition

A polymerization initiator composition, comprising an azobisamidine salt represented by the general formula (1) (1) wherein R1 and R2 independently represent an alkyl group or a cycloalkyl group, providing that R1 and R2 may together form an aliphatic ring, and Y represents -C(=NR3)-NH-R4 or a guanyl group represented by the formula (2) (2) wherein R3 and R4 independently represent a hydrogen atom, an alkyl group, a substituted alkyl group, a cycloalkyl group, an allyl group, a phenyl group, or a substituted phenyl group, R5 represents a lower alkylene group optionally containing a substituent group, and R6 represents a hydrogen atom or a hydroxyalkyl group, and X represents a chlorine atom, a bromine atom, or a CH3COO- group, and a hydrophilic organic compound.