conversion device turns off the swing side inverter 121 in which failure has occurred s 504 in this case the swing motor 120 is regenerated due to the inertial energy of the swing body s 506 in addition in the first exemplary embodiment the electric power conversion device turns off the engine side inverter 111 and operates the ultracapacitor side converter 131 s 508 next the electric power conversion device performs vdc voltage control of the ultracapacitor side converter 131 s 510 and stores the inertial energy of the swing body in the ultracapacitor 130 accordingly the electric power conversion device absorbs the inertial energy of the swing body while stabilizing vdc s 512 meanwhile in order to reduce time for deceleration of the swing body the electric power conversion device may operate the mechanical hydraulic brake which is provided in the swing motor 120 so as to allow the swing body to be stopped s 514 fig6 and 7 are an explanatory view and a flowchart of a second exemplary embodiment regarding an emergency stop process at the time of the swing side failure according to the present disclosure as illustrated in fig6 and 7 the electric power conversion device confirms that the swing side failure failure in the swing motor 120 or the swing side inverter 121 occurs s 702 further the electric power conversion device turns off the swing side inverter 121 in which failure has occurred s 704 in this case the swing motor 120 is regenerated due to the inertial energy of the swing body s 706 in addition in the second exemplary.