A supporting mechanism supports first and second exhaust treatment devices for treating exhaust gas from an engine, and includes a sub-bracket, a base bracket, and first and second supporting members. The base bracket includes first and second connecting parts, and first and second pipe members. The sub-bracket supports the first and second exhaust treatment devices. The base bracket supports the sub-bracket. The first and second supporting members respectively support one side and the other side of the base bracket. The first and second connecting parts are respectively joined to the first and second supporting members. The first and second pipe members are installed between the first and second connecting parts. The sub-bracket is attached to the first and second pipe members, extends in the lateral direction of the first and second pipe members, and is separated from the first and second connecting parts.