An intake device of an engine includes an air cleaner and an air flow sensor. The air cleaner includes an air filter, a cleaner case which forms a primary side space above the air filter and a secondary side space below the air filter, an inlet duct, and an outlet duct. The air flow sensor is fixed to the outlet duct. The cleaner case has a first side wall on which the inlet duct is mounted, and a second side wall which opposedly faces the first side wall. The air filter has a folded shape like bellows, and is held in the cleaner case. The second side wall has a deflecting portion which deflects air introduced from the inlet duct into a flow directed in an obliquely upward direction.