Power-up of gyrotrons was carried out and corresponding launcher systems were designed for plug and central-cell ECRH systems in the GAMMA 10 tandem mirror. Then, a high-power ECRH experiment was started. For the plug ECRH, new 500-kW gyrotrons produced a new record value of the confining potential. For the central-cell ECRH, development of a new antenna system has increased the transmission rate of incident microwave power and focused it onto the machine axis in the resonance surface. As a result, a clear increase of the diamagnetism was observed during the pulse of ECRH.