Air intake system for engine

In an air intake system for a multi-cylinder in line engine (2) mounted transversely in an engine compartment (1), intake branch pipes of an intake manifold (4,9) extended rearward of the vehicle over the cylinder head cover (3) from intake ports formed in the vehicle front side face of the engine are respectively offset frontward of the engine against spark plug units (31) projecting upward from the cylinder head cover (3), and at least a part of each intake branch pipe (41,91) overlaps vertically when viewing the engine form the rear side. An air cleaner unit (6,10) is arranged above a transmission (2) on the rear side of the engine (2).