An intake manifold includes a surge tank, and an intake passage part. An inner surface of the intake passage part includes: an inner peripheral region which is located inner side of the intake passage part in a curvature radius direction; an outer peripheral region which is located outer side of the intake passage part in a curvature radius direction; a first lateral region; and a second lateral region. The outer peripheral region includes a first inclined region, a second inclined region, and a bottom region. When seen in the section orthogonal to a center axis of the intake passage part, the first and second inclined region are curved so as to be convex outward from the intake passage part at a curvature radius. The bottom region has a shape convex outward from the intake passage part in the direction of the curvature radius.