To provide a polymer which has no anisotropic properties while retaining such features of a rigid linear polymer as a high elastic modulus, a low linear expansion coefficient, high resistance to heat, etc.

The branched polymer compound is a polymer formed by polymerizing at least one kind of a monomer selected from a group of substituted compounds of benzene, naphthalene and triphenylene each having three to six of -OH, -COOH and -OCOCH3 groups and at least one kind of a monomer selected from (1) an aromatic dihydroxy compound, (2) an aromatic dicarboxylic acid, (3) an aromatic hydroxycarboxylic acid, (4) an aromatic diamine, aromatic hydroxydiamine and an aromatic aminocarboxylic acid, and is characterized by having, as a starting point of the branch, a constitutional unit derived from the monomer selected from the group of substituted compounds of the above benzene, naphthalene and triphenylene.