The oscillator-type mid-infrared free-electron laser at Kyoto University named Kyoto University FEL (KU-FEL) has achieved the extraction efficiency of 9.4%* and the micro-pulse duration of 4.2 cycle** with the electron bunch charge of about 200 pC by the photocathode operation of 4.5-cell thermionic RF gun. Then the micro-pulse energy obtained was 100 micro-J. A new and dedicated 1.6-cell RF gun for the photocathode operation was fabricated and installed for increasing the electron bunch charge up to 1 nC and increasing the micro-pulse energy up to 1 mJ. The RF gun has curved cavity profile and elliptical cross-section of the connection between the half and full cell with a demountable cathode. This cavity design reduces the surface field of the inner cavity wall***. This improvement is important for having long macro-pulse (~10 micro-s) operation of the gun, which is essential for the oscillator-type FEL. The commissioning of the RF gun is undergoing. Results of commissioning experiments will be presented in the conference.