<p>A controller (7) outputs an operational instruction (10A), which represents a new engine speed, to an engine generator (1) based on power supply conditions from the engine generator (1) to a common bus (9) or on operating conditions of a crane device. As a result, the engine speed is regulated in response to a variation in the load side devices such as electric motors (30-33). This significantly reduces operational costs of the crane device.</p>
