A swiveling body is installed on a base in a swivelable manner. An electric motor for swiveling swivels the swiveling body. An inverter supplies electric power to the electric motor for swiveling. An obstacle detector detects an obstacle around the base and transmits a detected result to a control unit. When the obstacle detector detects the obstacle, the control unit determines whether or not the obstacle is present within a monitoring region, and when the obstacle is present inside the monitoring region, the control unit stops the electric motor for swiveling. In order to avoid danger, the swiveling operation can be stopped more safely.