To make a forward/reverse turn angle by a cylinder device 180 degrees or more in a turn unit.

Between a turning body 1 and a fixed part 3, a pair of cylinder devices 10, 15 connected to the turning body 1 by a common connecting shaft 8 are arranged, the turning body 1 can be right/left turned at a large turn angle of 180 degrees or more. In both the cylinder devices 10, 15, by switching a hydraulic circuit, extension/contraction driving in a reverse direction to each other and in the same direction is simultaneously performed, by simultaneous driving of this cylinder device 10, 15, even in both right/left turns of the turning body 1, sufficient turn drive force is obtained.