The next generation light source such as X-ray FEL oscillator requires high brightness electron gun with megahertz repetition rate. We have developed a photoemission DC gun at JAEA. By employing a segmented insulator with guard rings, we successfully applied 500 kV on the ceramics with a central stem electrode for eight hours without any discharge in 2009. In 2011 we reached 526 kV with NEG pumps and electrodes in place, before suffering another field emission problem from the cathode electrode. The problem may be attributed to small dust inside our gun chamber. We also generated high current beam up to 10 mA and obtained charge extracted lifetime of 30 C. In this paper, our current status of development will be presented.