To avoid such a trouble that the control of a work unit is disabled by the failure of an electric detector or the breakage of an electric wire to the electric detector by eliminating the need of installing the electric detector for detecting the position of the work unit on the work unit side when work unit controls such as interference avoidance control and position limit control are performed based on the position of the work unit.

Cameras 42A and 42B photographing the work unit and a control part 32 calculating the position of the work unit based on image signals from the cameras 42A and 42B are installed on a machine body, and the interference avoidance control and position limit control are performed based on the calculated position of the work unit.