Remote handling (RH) system is necessary for the maintenance and repair of in-vessel components of JT-60SA. Design study of RH system, focusing on the deployment of the toroidal rail and replacement of the lower divertor cassettes, is described in this paper. The space for RH system is very limited inside the vacuum vessel and horizontal port. The RH rail is installed before transporting divertor cassettes. The RH rail, which is coupled with six pieces and three-point mounting, can cover 180 degrees in toroidal direction. A divertor cassette can be replaced by vehicle manipulator that consists of an end effector, a telescopic arm and a vehicle. The vehicle manipulator brings the divertor cassette to the front of another horizontal port, which is used for supporting the rail and/or carrying in and out equipments. Then another RH device, which is installed from outside the vacuum vessel, receives and brings out the divertor cassette. The basic designs of RH system for deployment of the RH rail and replacing lower divertor cassettes are established.