A research project for developing a thunder lightning control system using an induction linac based high power microwave free electron laser (FEL) was started at JAERI. The system will produce a weakly ionized plasma rod in the atmosphere by high power microwaves and control a lightning path, away from, e.g., nuclear power stations and rocket launchers. It has been known that about 1 MW/cm 2 power density is enough for the atmospheric breakdown in the microwave region, which means that a high power microwave FEL with GW level output power is feasible for atmospheric breakdown, and accordingly is feasible for a thunder lightning control tool by making a conductive plasma channel in the atmosphere. From the microwave attenuation consideration in the atmosphere, FELs of 35 GHz (0.13 dB/km), 90 GHz (0.35 dB/km), 140 GHz (1.7 dB/km), and of 270 GHz (4.5 dB/km) are the best candidates for the system. Compared with other proposed lightning control systems using a visible or an ultraviolet laser, the system using microwave has the advantage that microwave has a smaller attenuation with rain or snow which always exists in the real atmospheric circumstances when lightning occurs. A detailed description and feasibility study of the system will be given.