PURPOSE: To provide a device whereby accelerating an existing ship can be attained by additionally providing a propulsive power auxiliary engine, and mechanically connecting an output of this auxiliary engine to a propeller shaft, so as to realize high transmitting efficiency and the simple device, in the existing ship having a slow ship speed.

CONSTITUTION: In a gear device 4, a cargo hold 1 or a tank and the like of an existing ship are modified here to arrange a propulsive power auxiliary engine 2, and its output is designed so as to obtain desired acceleration/ deceleration ratio and an output direction, and when necessary, another gear device 5 and a shaft system 6 are provided and mechanically connected through a clutch 3 to a propeller shaft 8 having a propeller 11 capable of changing a propeller blade angle.