The control system of J-PARC project is under construction. After almost finishing the hardware installation of the L3BT section, an online device commissioning was performed for magnet power supply, stepping motor and vacuum system. Many components for device control have already been developed separately, but not integrated together yet. It is the first experience to combine all the components, including core software for a front-end IO controller, an EPICS run-time database, and a remote graphic user interface. This paper describes the detail of the recent construction status of the L3BT control system, including component development, system integration, and device commissioning.