To easily and surely fit an outboard engine fitting base.

An outboard engine fitting base B to be installed in an air barrel (a) of an inflatable boat A is provided with a vertical support plate b1, to which an outboard engine C is fitted, and a horizontal support plate b2 fitted to the vertical support plate b1 for support. This outboard engine fitting base B has a first lock means 1 for attaching and detaching the vertical support plate b1 to/from the air barrel (a) and a second lock means 2 for attaching and detaching the horizontal support plate b2, and the first lock means 1 is formed of an insertion piece 1a and a lock groove body 1b, and the second lock means is formed of a similar insertion piece and a lock groove body. The insertion pieces 1a of both the first and the second lock means are inserted into the lock groove bodies 1b for engagement, and the fitting base B is thereby fitted to the air barrel (a) freely to be removed.