PURPOSE: To allow bearing of load commensurable with the characteristics of propeller over the entire speed range of an electric propulsion vessel employing a variable speed drive system by controlling two propeller speeds and outputs.

CONSTITUTION: Two sets of variable speed driving systems, comprising motors 5a, 5b and power converters 6a, 6b, are mounted for one double contrarotating propeller unit 3 thus constituting an electric propulsion system. The motor 5a driving the first propeller of the double contrarotating propeller unit 3 is subjected to rotational speed control according to a rotational speed command for propeller by means of the first power converter 6a. The motor 5b for driving the second propeller rotating reversely to the first propeller is subjected to output control according to a motor output command by means of the second power converter 6b. This constitution allows bearing of load commensurable with the characteristics of the propeller unit 3 over the entire speed range.