To reduce the height of a crankcase by arranging a communicating passage in a proper position and to miniaturize an engine in a multi-cylinder internal combustion engine provided with an upper crankcase integrated with a cylinder block or provided separately from the cylinder block on the downside of the cylinder block and a lower crankcase connected to a lower part of the upper crankcase and provided with a communicating passage that communicates with internal spaces of plural crank chambers corresponding to plural cylinders. In the multi-cylinder internal combustion engine, a communicating hole that communicates with the communicating passage is provided on at least either side of the upper crankcase or the lower crankcase, and a cover forming the communicating passage is arranged with the cover covering the communicating hole and is attached to both crankcases across a joined plane of the upper crankcase and the lower crankcase.