Generally, when the reverse-parallel thyristor pairs are applied to the 3 phase star-connected circuits, the regulating behavior is considerably complicated. At the inductive load, if the gate-pulse width to the thyristors is unsuitable, the regulating voltage characteristics become discontinuous. In cases of the resistive and inductive loads, we have investigated chiefly by means of the graphycal analysis the effects of the gate-pulse width on the output voltage wave forms. And thus, the relationships between the gatepulse width and the regulating voltage characteristics became clear. As the result, in order to remove the discontinuity of the regulating voltage characteristics, it is necessary to use the gate-pulse which is a pair of double pulse generated at an interval of 60 electrical degrees and the each individual pulse forming it has a width of 60 electrical degrees. The above analytical results are confirmed experimentally.