To correct output characteristics of an A/F ratio sensor, which have been deviated caused by in-cylinder injection by controlling a fuel injection timing of a specified cylinder with an A/F ratio sensor so that an output change position of the A/F ratio sensor closes to the position of the stoichiometric A/F ratio, and thus permitting adequate feedback control.

An outboard unit 1 has a 2-cycle 6 cylinder in-cylinder injection engine 2. To a control unit 29, detection signals indicating status of the outboard unit 1, the engine 2, and the ship from various sensors, at least those from an A/F ratio sensor 105 detecting an air fuel ratio within a #1 cylinder 7a which is located at the uppermost stage are input. The control unit 29 outputs control signals at least to a fuel injection valve 13. The #1 cylinder 7a relatively advances a fuel injection timing so that sufficient injected fuel reached a collection hole serving as a detection hole of the exhaust gas. With this, sufficient unburned gas reaches at the sensor part of the A/F ratio sensor, thereby the changing position of the sensor output characteristics closes to the position of the stoichiometric A/F ratio.