Flicker may be caused by “frequency feedback method with step injection of reactive power” installed in PCS which is generally used as grid-connected inverter in Japan. Therefore, in this paper, characteristics of the flicker were investigated by experiments with actual PCS in single phase circuit. Furthermore, effective means for suppressing the flicker was considered by taking the cause of occurrence of flicker into account. Moreover, it was clarified the differences among PCSs on flicker using multiple actual PCSs. In conclusion, gain of frequency feedback function should be reduced as one of effective means to avoid flicker.