The steering ECRH antenna system has been developed and is in operation for the GAMMA 10 plasma experiment for efficient electron heating. The steering antenna can be shifted vertically as -10 ~ +10 mm from the standard setting. The plasma experiments with the installed antenna show that the steering system works appropriately. From the examined experiments of the antenna position scan, power scan etc, it is found that the effective heating requires the precise and delicate setting of the injection beam. The lowest antenna position in the standard setting gives the highest diamagnetism rise of 9 %, and the rise rate increases in accordance with the power.