A high strength gear used as an element of a power transmission mechanism. The gear includes a base gear formed of an iron-based alloy subjected to carburizing or carbonitriding treatment. The base gear has an engaging surface with which an opposite gear is engaged. The engaging surface of the base gear is coated with a first diamond-like carbon film which has a hydrogen content of not more than 10 atomic % and a surface hardness ranging from 8 to 30 GPa in a nano-indentation test. Additionally, at least a part of the first diamond-like carbon film is coated with a second diamond-like carbon film which has a hydrogen content of not more than 10 atomic % and a surface hardness ranging from 50 to 90 GPa in the nano-indentation test. The second diamond-like carbon film has a surface roughness Ra ranging from 0.1 to 0.2 μm.