Abstract: An organopolysiloxane which forms a cured product having a high refractive index, high transparency, and excellent heat resistance when subjected to a hydrosilylation reaction and which is represented by the following average unit formula: (R13SiO1/2)a(R12SiO2/2)b(R2SiO3/2)c(SiO4/2)d wherein, R1 are alkyl groups, alkenyl groups, phenyl groups, or hydrogen atoms; R2 is a group represented by R1 or a condensed polycyclic aromatic group or a group containing a condensed polycyclic aromatic group, but at least one of R1 or R2 in a molecule is an alkenyl group or a hydrogen atom, at least one R2 in a molecule is a condensed polycyclic aromatic group or a group containing a condensed polycyclic aromatic group; and a, b, c and d are numbers that satisfy: 0.01?a?0.8, 0?b?0.5, 0.2?c?0.9, 0?d<0.2 and a+b+c+d=1.