There is provided a slewing control device that enables to detect breakdown of a driving system of a mechanical brake, and generate a torque for holding a slewing body in a stopped state to thereby prevent movement of the slewing body when an anomaly has occurred. In a working machine for driving a slewing body by an electric motor 1, judgment is made as to whether a mechanical brake 4 is in an inconsistent state, based on a command to be outputted to a brake circuit B, and a pressure detected by a brake pressure sensor 17. The inconsistent state is a state that the mechanical brake 4 is in a brake released state when an activation command for switching the mechanical brake 4 to a brake activated state is outputted. If it is judged that the mechanical brake 4 is in the inconsistent state, a command for obtaining a braking torque for holding the slewing body in a stopped state is outputted to the electric motor 1.