A copolymer comprising structural units derived from ethylene, an α-olefin having 3 to 20 carbon atoms, a nonconjugated polyene [C-1], in which among carbon-carbon double bonds, only one carbon-carbon double bond polymerizable with a metallocene catalyst is present in one molecule, and a nonconjugated polyene [C-2], in which among the carbon-carbon double bonds, two carbon-carbon double bonds polymerizable with the metallocene catalyst are present in one molecule, and being synthesized through the use of the metallocene catalyst, wherein the nonconjugated polyene [C-1], in which among carbon-carbon double bonds, only one carbon-carbon double bond polymerizable with the metallocene catalyst is present in one molecule, is 5-ethylidene-2-norbornene, and the nonconjugated polyene [C-2], in which among the carbon-carbon double bonds, two carbon-carbon double bonds polymerizable with the metallocene catalyst are present in one molecule, is 5-vinyl-2-norbornene, wherein the structural units derived from the α-olefin having 3 to 20 carbon atoms constitute 10 to 50 percent by mole in 100 percent by mole of the total structural units, the total of the percent by mole of the structural units derived from the nonconjugated polyene [C-1], in which among carbon-carbon double bonds, only one carbon-carbon double bond polymerizable with the metallocene catalyst is present in one molecule, and the percent by mole of the structural units derived from the nonconjugated polyene [C-2], in which among the carbon-carbon double bonds, two carbon-carbon double bonds polymerizable with the metallocene catalyst are present in one molecule, is 1.0 to 6.0 percent by mole, the ratio ([C-1]/[C-2]) of the percent by mole of the structural units derived from the nonconjugated polyene [C-1], in which among carbon-carbon double bonds, only one carbon-carbon double bond polymerizable with the metallocene catalyst is present in one molecule, to the percent by mole of the structural units derived from the nonconjugated polyene [C-2], in which among the carbon-carbon double bonds, two carbon-carbon double bonds polymerizable with the metallocene catalyst are present in one molecule, is 75/25 to 99.5/0.5, the Mooney viscosity [ML (1 + 4) 100°C] measured at 100°C is 10 to 200, and the activation energy of fluidization (Ea) of the copolymer satisfies the following formula: 50 > Ea kJ / mol > 35 measured as disclosed in the description. the structural units derived from the α-olefin having 3 to 20 carbon atoms constitute 10 to 50 percent by mole in 100 percent by mole of the total structural units, the total of the percent by mole of the structural units derived from the nonconjugated polyene [C-1], in which among carbon-carbon double bonds, only one carbon-carbon double bond polymerizable with the metallocene catalyst is present in one molecule, and the percent by mole of the structural units derived from the nonconjugated polyene [C-2], in which among the carbon-carbon double bonds, two carbon-carbon double bonds polymerizable with the metallocene catalyst are present in one molecule, is 1.0 to 6.0 percent by mole, the ratio ([C-1]/[C-2]) of the percent by mole of the structural units derived from the nonconjugated polyene [C-1], in which among carbon-carbon double bonds, only one carbon-carbon double bond polymerizable with the metallocene catalyst is present in one molecule, to the percent by mole of the structural units derived from the nonconjugated polyene [C-2], in which among the carbon-carbon double bonds, two carbon-carbon double bonds polymerizable with the metallocene catalyst are present in one molecule, is 75/25 to 99.5/0.5, the Mooney viscosity [ML (1 + 4) 100°C] measured at 100°C is 10 to 200, and the activation energy of fluidization (Ea) of the copolymer satisfies the following formula: 50 > Ea kJ / mol > 35 measured as disclosed in the description.