The bottle neck of the realization of large-scale UAM is the power source, and there is eagerly expected for the development of a high-performance power source to replace lithium batteries. Next-generation hybrid power systems consisting of gas turbine generators with high-efficiency power supply capability and lithium batteries with excellent instantaneous power supply capability are considered to be the mainstream of next-generation power sources. In order to meet the large UAM power requirements, ADJ is developing a maximum output 30 kW class gas turbine generator, which is the heart part of the hybrid power system. It is currently in the final stage of development, and the first gas turbine generator functional testing was conducted in June 2022. The GT/GEN development is scheduled to be completed in December 2022. This paper describes the background to the development of gas turbine generators, trends in the development of next-generation UAMs, market size forecasts, the development status of gas turbine generators in ADJ, and the ADJ GT/GEN lineup plan.