To provide a conjugated diene rubber forming a vulcanized rubber having excellent reinforcing effects with a reinforcing agent such as silica and excellent low heat build-up and wet gripping properties and abrasion resistance.

The conjugated diene rubber is obtained by reacting a polymer prepared by polymerizing a monomer mixture containing a conjugated diene monomer using an organic active metal as an initiator and having active terminals with a coupling agent. Furthermore, the coupling agent is a functional group-containing hydrocarbon polymer comprising a monomer unit having at least one kind of functional group selected from the group consisting of an epoxy group, a carboxy group and an amino group and present in a number of ≥5 per molecule of the polymer and having 300-100,000 number-average molecular weight.