To provide a cooling water passage washing device for an outboard motor high in usage property and handling property and capable of ensuring good appearance.

The cooling water passage washing device is covered with an engine cover constituted by an upper cover 112 and a lower cover 113 capable of being vertically divided. A washing water introduction port 11 is provided on a front surface of the lower cover 113 and the washing water introduction port 11 and the cooling water passage of the engine are connected through a connection hose. The lower cover 113 is constituted by a front cover 113A fixed to a front part of the engine and a pair of side covers 113B fixed to both sides of the engine. The washing water introduction port 11 is provided on the front cover 113A.