A dual frequency (110 GHz and 138 GHz) ECRF system development began for JT-60SA. A gyrotron output power and efficiency higher than 1 MW and 30% with a peak heat load at cavity lower than 1.4 kW/cm2 were obtained for both frequencies in calculation. Mode conversion efficiency of the quasi-optical mode converter sufficiently high for long pulse operation at 1 MW (96.8% for 110GHz and 98.3% for 138GHz) was also obtained in calculation. In the first conditioning operation of the newly fabricated gyrotron, an output power of 1.1 MW was obtained for 100 ms with an efficiency of 32% at 110 GHz.