A block copolymer comprising two or more blocks and having fluorescence in the solid state, wherein blocks thereof may be the same or different, and in each of the blocks, one or more kinds of repeating units are bonded through conjugated bonds, and bonding between the blocks is made by junction unit having conjugated bond, and the polystyrene reduced number average molecular weight of at least one block is 1.times.10.sup.3 to 1.times.10.sup.8.