An air intake device for a watercraft adapted to suppress noise generating from an intake system of an engine and can obtain good intake efficiency. The air intake device includes intake ports opening to a side surface of the engine, and an air cleaner located on the rear side of the engine. An outlet of the air cleaner is connected through an intake passage to the intake ports of the engine. An air duct extends from an inlet of the air cleaner along the side surface of the engine to the position corresponding to the front end of the engine. The air duct has a front opening that faces downward.