A composition includes two types of polymers each having a different weight average molecular weight. The two types of polymers are each a styrene polymer having a group which bonds to at least one end of a main chain and which includes at least one of a hydroxy group, a carboxy group, a sulfanyl group, an epoxy group, a cyano group, a vinyl group or a carbonyl group. A difference in weight average molecular weight between the two types of polymers is no less than 2,000 and no greater than 30,000.