The present invention provides a novel silicon compound represented by Formula (1) having a living radical polymerization initiating ability for addition-polymerizable monomers and a polymer obtained using the same. The above polymer can provide an organic-inorganic composite material having a distinct structure. wherein R1 is hydrogen, alkyl, aryl or arylalkyl; R2 and R3 are alkyl, phenyl or cyclohexyl; and A is a group having an ability to initiate polymerization of a monomer.