A polymeric polymerization initiator represented by the following formula (I). M1aM2bD1cD2dT1eT2fQg (I) M1=R13SiO1/2 M2=R12R2SiO1/2 D1=R12SiO2/2 D2=R1R2SiO2/2 T1=R1SiO3/2 T2=R2SiO3/2 Q=SiO4/2 [R1 represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. R2 represents a group having a ketene silyl acetal structure represented by the following formula (II). (A represents a single bond or a divalent organic group, R3 represents a hydrogen atom or a substituted or unsubstituted alkyl group, and R4 represents a substituted or unsubstituted alkyl group.) “a”, “b”, “c”, “d”, “e”, “f”, and “g” represent 0 or a positive integer where b+d+f≥1. An order of bonding of siloxane units is optionally determined.]