In an electric rotary excavator (construction machine) 1, when earth
pressure acts on a rotary body 4 in an opposite direction to an
instructed direction of a lever, a control-system changing means 150 of a
rotation control device 100 increases a torque output of an electric
motor 5 that drives the rotary body 4. Accordingly, the torque output can
properly react against the acting earth pressure, thereby preventing the
rotary body from continuing to be rotated in the opposite direction.
Therefore, even when the earth pressure becomes large, the work will not
be affected. In addition, when the rotary body is rotated on a slope, the
rotary body can be prevented from being rotated back greatly due to the
weights of the boom and the arm.