PURPOSE: To aim at simplification in a hydraulic circuit in terms of structure, by connecting a hatch cover on-off gear driving circuit to a deck machine driving circuit for a crane or a winch, etc., via a booster side hydraulic motor and a driving side hydraulic motor both being installed in parallel with the deck machine driving circuit, while coupling its return flow passage with the driving side hydraulic motor.

CONSTITUTION: A hatch cover on-off gear driving circuit 4 is set up in position between each of deck machine driving circuits 2 and 3, and at this time, a booster side hydraulic motor 11 and a driving side hydraulic motor 12, coupling each of output shafts 13 and 14, are parallely installed via a coupling 15, then a return flow passage 28 of the hatch cover on-off gear driving circuit 4 is connected to the driving side hydraulic motor 12. With this constitution, low pressure and large capacity hydraulic pressure at these deck machine driving circuits 2 and 3 drives the driving side hydraulic motor 12 with a part of its large capacity via the return flow passage 28, and the booster side hydraulic motor 11 is driven by the coupling 15 whereby high pressure and small capacity hydraulic pressure comes possible to be fed to the hatch cover on-off gear driving circuit 4. Therefore, simplification in a hydraulic circuit is thus promotable without using a special something for each hydraulic machinery and equipment.