In a blowby gas treatment system for a multiple cylinder engine, in which: a first cylinder and a second cylinder are provided to the engine; a first fuel supply device that always operates during operation of the engine is connected to the first cylinder; and a second fuel supply device that is capable of stopping an operation thereof during the operation of the engine is connected to the second cylinder, first and second branch pipes of an intake manifold are connected to the first and second cylinders, and a blowby gas outlet of a breather chamber and a blowby gas inlet opening into the first branch pipe communicate with each other via a breather pipe, the breather chamber collecting a blowby gas of the engine. Accordingly, when any of the cylinders is stopped, it is possible to easily prevent a blowby gas from flowing toward the stopped cylinder.