Recent progress on the development of a high power 170 GHz gyrotron obtained in Japan Atomic Energy Agency (JAEA) is presented. A 5 kHz, 1.1 MW power modulation was demonstrated at CW mode with a full beam current modulation by the anode voltage switching of the triode electron gun. Because of the full beam modulation, collector heat load was significantly reduced. In the voltage rise-up phase of each pulse, adjacent lower mode is excited. To decrease the time duration of this unwanted mode, double anode switch is proposed to minimize the influence of stray capacity that lengthen the time constant of the circuit. In the dual frequency gyrotron development, the 1.3 MW oscillations at 170 GHz and 137 GHz were successfully demonstrated by changing the resonator field, gun field. Here, anode voltage of the triode gun is optimized to obtain the optimum pitch factor of the beam keeping the beam voltage constant. The coupling experiment of the output power to the waveguide of 63.5mm in diameter was carried out. At the input of the waveguide, 95 % of the HE11 content was obtained. The RF power was transmitted to the 40 m corrugated waveguide system with 7 miter bends, and 91 % of the HE11 mode content is demonstrated at the end of the transmission line.
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