[en] J-PARC 3GeV Synchrotron (RCS) started beam commissioning in 2007. The beam commissioning has been continued to increase the beam power for users. In a high-intensity hadron accelerator such as J-PARC, it is essentially important to reduce the activation due to the beam loss and to suppress the exposure of workers. For this purpose, RCS has continued to study and countermeasure for the causes of the beam loss from the initial stage of beam commissioning. At present, stable user operation is continuing at 500 kW. This value is half of the design beam power of 1 MW, and the residual doses are being maintained enough small so that the maintenance work does not be hindered. In this report, we introduces the history and measures of the residual doses in RCS so far, and the situation of the exposure dose of workers during maintenance work. (author)