[en] In J-PARC main ring, each of the main magnets (Bending, Quadrupole, Sextupole) has a trim-coil. The basic aim of trim-coil is to correct small deviation of each magnetic field. In addition, we have used them for other purposes, for example: (1) in Beam-Based-Alignment studies, (2) as flux monitors, and (3) to make a short-circuit to reduce ripples of magnetic field. At a moment, trim-coils can be used for only one purpose. We introduced relay-switches to change trim-coil connection to a device, which corresponds to the selected purpose. When we switch the purpose, we have to change 1,200 on-site relays manually, distributed in three buildings. Thus, a control system for trim-coil relay-selectors have been developed in winter, 2014-2015. EPICS tools and environment are used to develop the system. The system comprises PLC I/O modules with controller running EPICS on Linux. The system will be in operation after March, 2015. By using the system, we expect much easier switching of relay-switches than before. (author)