The L-band photo-cathode RF gun is being developed for the L-band electron linac at Osaka University, which also meets the specifications for the International Linear Collider Project. The critical issue of the RF gun is the high average power input. The cooling-water system of the RF gun cavity is designed and its performance is studied with simulation for thermal analysis. It is shown that the cooling system works well as designed. The DESY-type L-band RF gun is being commissioned at KEK. Reported are the present status of the commissioning of the RF gun and the construction of the injection beam line of the Superconducting RF Test Facility at KEK.