A novel olefin-based polymer has excellent thermal resistance, as well as excellent balance among various properties. The olefin-based polymer is an olefin-based polymer comprising 50 to 100% by weight of a constituent unit derived from 4-methyl-1-pentene, and 0 to 50% by weight of a constituent unit derived from at least one olefin selected from olefins having 2 to 20 carbon atoms except 4-methyl-1-pentene, and having the following properties: i) the diad isotacticity is 70% or greater, ii) the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) as measured by gel permeation chromatography (GPC) is in the range of 1.0 to 3.5, and iii) the intrinsic viscosity [η] is 0.5 (dl/g) or greater.