We have developed an Electron Tracking Compton Camera (ETCC) as an MeV gamma-ray telescope in the next generation. The ETCC consists of a gaseous time projection chamber and a position sensitive scintillation camera. We had launched a small size ETCC loaded on a balloon in 2006, and it was successful to obtain the fluxes of diffuse cosmic and atmospheric gamma rays in the energy range between 125 keV and 1.25 MeV. As the next flight (SMILE-II), we planned a long duration flight using a circumpolar balloon launched from Kiruna, and it will observe the celestial bright sources and the atmospheric gamma-ray burst due to the relativistic electron from the radiation belt. In this paper, we report the concepts of our detector and the performance of the SMILE-II prototype.