To provide a ship propulsion mechanism capable of increasing the propulsive force of a ship without interference of eddy currents of propellers with each other.

An engine for outputting the rotational power to each auxiliary propulsion propeller is arranged inside a ship bottom part between a main propulsion propeller and right and left auxiliary propulsion propellers. The ship bottom part with the engine being arranged therein is raised downwardly in the projecting shape, and a bottom part of each engine is located in the raised space. Thus, the auxiliary propulsion propeller can be arranged above the main propulsion propeller at the position as high as possible, the propeller shaft does not form any propulsive obstacle. Further, the ship bottom has a forwardly projecting shape and backwardly recessed shape, and the propulsive force can be demonstrated without canceling the propulsive force without interference of eddy currents of the propellers with each other.