TECHNOLOGY FOCUS - POLYMERS - Preferred Polymer: The (pi)-conjugated system tree-like branch compound is a (pi)-conjugated polymer having a tree-like branch in core unit in principal chain and the side chain which is coupled, where n is an integer greater than 1. The polymer has tree-like branch in the side chain. The branch unit except terminal branch unit and core unit are multivalent groups induced from an aromatic ring or an aromatic heterocyclic ring. The terminal branch unit is a univalent group induced from an aromatic ring or an aromatic heterocyclic ring. The coupling of core unit and branch unit and the coupling of branch units are by a single bond, in polymer having tree-like branch in the side chain. A terminal branch unit is a (pi)-conjugated polymer having at least one group chosen from hydrogen atom, alkyl group, substituted or unsubstituted amino group, alkoxy group and alkylthio group, and having a tree-like branch in the side chain. The principal chain of (pi)-conjugated polymer is polyphenylene vinylene type-polymer, polyphenylene ethynylene type-polymer, poly fluorene type-polymer, polythiophene type-polymer, polythiadiazole type-polymer or polyparaphenylene polymer, having a tree-like branch in the side chain. The (pi)-conjugated polymer contains a repeating unit of formula (1) and has a tree-like branch in a side chain.R1,R2=H, alkyl group, univalent heterocyclic group or cyano group;Ar=group induced from aromatic ring or aromatic heterocyclic ring;p=o or 1;q=1-6;andG=univalent group induced from (pi) conjugated system tree-like branch compound (where n is two or more).The branch unit except terminal branch unit and core unit are trivalent groups induced from substituted or unsubstituted benzene. The (pi)-conjugated polymer has polystyrene conversion weight average molecular weight of is 3000-5 million. Preferred Electroluminescent Element: The organic electroluminescent element is equipped with a layer containing (pi)-conjugated polymer having a tree-like branch in the side chain, as a light emitting layer. A dopant is added to the base material containing (pi)-conjugated polymer having a tree-like branch in the side chain. EXAMPLE - A tertiary butyl compound and 18-crown-6-ether were dissolved in toluene. An intermediate of formula (d1-3), which was synthesized using a side-chain compound of formula (a1-3), was dissolved in toluene and dripped slowly. Stirring was performed for 3 hours or less, in nitrogen atmosphere. The obtained reaction liquid was introduced into methanol, precipitated, washed and dried, to obtain a (pi)-conjugated polymer (PPV 2-1) having second generation tree-like branch compound in a side chain. The obtained polymer had excellent solubility and a glass transition temperature of 223degreesC. Using the obtained (pi)-conjugated polymer, an organic electroluminescent element having luminescence of 413 cd/m2 at current density 10 mA/cm2, drive voltage of 3.86 V and brightness reduction-by-half lifetime of 500 hours at current density 10 mA/cm2, was obtained efficiently.