PURPOSE: To accelerate photoiniferter polymerization by adding a specified metal compound.

CONSTITUTION: An iniferter (example: cyclohexane monoiniferter which forms a terminator free radical and an initiator free radical when exposed to an appropriate energy source is prepared. Next, the iniferter is mixed with the first monomer inputting substance containing free radical polymerization monomer (example: methyl methacrylate) and exposed to an appropriate energy source to form a free radical copolymer segment. Moreover, the second monomer inputting substance containing a free radical polymerization monomer is added and exposed to an energy source to form a block copolymer. On this occasion, a metal compound (example: 2-ethylhexane tin (II) expressed by a formula MxLz (M is metal such as tin, zinc, cobalt, and titanium; z is valency of metal; x is 1 or greater; L is 1-20 C alkyl, aryl, etc.), is added to a polymerization system as a polymerization accelerator.