To provide an ethylenic copolymer synthesizable by a single-stage reaction under a mild condition and exhibiting high crosslinkability to form a crosslinked product having excellent physical properties such as hardness and melting point.

The ethylenic copolymer contains a bivalent cyclic hydrocarbon group having an Si-containing substituent of the general formula: -Si(R1)(R2)(R3) (at least one of R1, R2 and R3 is a hydrolysable substituent reactive with water and the other groups are each independently H or a hydrocarbon group) as the 2nd monomer unit in a polymer chain containing ethylene group as the 1st monomer unit.