A new 5-cell cavity has been developed for the upgrade of the J-PARC Main Ring. In the cavity, high impedance magnetic alloy - Finemet FT3L, cores are loaded. The cavity was installed and has been used for the 250 kW beam operation. The cavity is operated with the RF voltage of 70 kV which is two times higher voltage than the present cavities. Eight more cavities will be assembled and installed in the next two years to increase the repetition rate of the Main Ring. This paper describes status of cavity operation under the beam loading and status of the mass productions of the cavities. Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA
