PURPOSE:To make maintenance easier by improving the durability of a spiral driver by a method in which a drive motor and an output unit are housed in one casing to make up a rotary coupler from the casing and the output unit. CONSTITUTION:An output unit 14 housed in a casing 12 is allowed to turn by a drive motor 13 set in the casing 12 having a fluid port 15 connected to an oil pressure source. The unit 14 has a flow path 16 leading to the port 15, and the path 16 is connected to a fluid port 17 through which pressure oil outside the output unit passes to make up a driver 11. The unit 14 is turned through a decelerating mechanism 18 by the motor 13, and a revolving superstructure is turned by torque generated. Regardless of the revolving motion, pressure oil is passed through the ports 15 and 16 and the path 16 between the fixed part actuator and the oil pressure source, permitting it to serve as a rotary coupler.
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