MODIFIED VINYLAROMATIC COPOLYMER, PRODUCTION METHOD THEREFOR, MODIFIED CONJUGATED DIENE COPOLYMER OBTAINED THEREFROM AND COMPOSITION THEREOF, CROSSLINKED RUBBER OBJECT, AND TIRE MEMBER

To provide a modified vinylaromatic copolymer which can be used in production of copolymer rubber and which has reactivity and solubility, and a copolymer rubber material obtained therefrom, which simultaneously has processability, strength, and homogeneity. The modified vinylaromatic copolymer is a copolymer containing a structural unit (a) derived from a divinylaromatic compound and a structural unit (b) derived from a monovinylaromatic compound, wherein the structural unit (a) at least partially includes the following crosslinked structural unit (a1), and a terminal is modified by a modification group having at least one functional group selected from the group consisting of an amino group, a hydroxyl group, and an alkoxysilyl group.