To provide a hydrocarbon resin for modifying a rubber composition that maintains piercing strength and tear strength of the rubber composition and at the same time exhibits an excellent improvement effect of wear resistance, elongation and productivity.

The ethylidene group-containing dicyclopentadiene-based hydrocarbon resin is produced by copolymerizing (1) 40-95 pts.wt. composition (composition A) comprising a cyclopentadiene-based compound having a specific structural formula and/or its Diels-Alder adduct, (2) 5-60 pts.wt. composition (composition B) comprising a 5-ethylidene norbornene-based compound having a specific structural formula, provided that the total of the composition A and the composition B is 100 pts.wt., and (3) 0-50 pts.wt. fraction (composition C) produced by thermal cracking of petroleums or the like and having a boiling point in a range of 140°C-220°C.