Provided is an intake manifold for an internal combustion engine, the intake manifold including an upstream portion, a first downstream portion, and a second downstream portion. The upstream portion includes a first upstream passage and a second upstream passage. The first downstream portion includes a first downstream passage configured to communicate the first upstream passage with an intake port of a first cylinder head. The second downstream portion includes a second downstream passage configured to communicate the second upstream passage with an intake port of a second cylinder head. The upstream portion, the first downstream portion, and the second downstream portion are provided in a separate manner. In the intake manifold, a flange of the first downstream portion is connected to a flange of the upstream portion, and a flange of the second downstream portion is connected to the flange of the upstream portion.