A ship powered by an internal combustion engine (1) and an electric motor (2) connected to a propeller (3) powered by surplus electric power obtained by a thermal discharge recovery system has a controller including a feedback control section for controlling a base amount of fuel injected to the internal combustion engine (1) based on the difference between the target number of rotation of the propeller given by the operator and the real number of rotation, and a feed-forward control section having a means (25) for calculating an overall power output and a means (26) for calculating a correction in the amount of fuel injected to the internal combustion engine based on the overall power output and the number of rotation of the propeller. The base amount of fuel is corrected by subtracting the correction obtained by the feed-forward section from the base amount of fuel calculated by the feedback control section whereby preventing a rapid change in the speed of the ship due to rapid change in ship loads.