An intake manifold (M) for a multi-cylinder internal combustion engine has a collection section (10) for forming an intake collection chamber (11) and also has a branch section (20) for forming an intake branch path (22). The collection section (10) is formed by joining first and second spaces (11a, 11b), which make up the intake collection chamber (11), to first and second cases (A, B). Corners (31a, 31b) are formed integrally with the first and second cases (A, B). In the second case (B) is placed a flow straightening section (40) extending across the inside of the first and second cases (A, B) and covering the inner surfaces (31a1, 31b1) of the corners (31a, 31b). The flow straightening section (40) has a guidance surface (44) for more smoothly guiding intake air than the inner surfaces (31a1, 31b1). Because the collection section of the intake manifold has a split structure, the flow of intake air in the intake collection chamber is smooth irrespective of the shape of the corners of the collection section, and this improves volumetric efficiency.