PURPOSE: To correct imbalance so as to minimize the total corrected amount, by dividing an imbalance vector into 2W4 vectors to a correctable direction corresponding to the magnitude of the imbalance vector.

CONSTITUTION: An imbalance vector is divided into two vectors in direction i1, i2 of correctable directions i1Wi4 at every 30°. When the divided vector in the direction i1 exceeds the correctable region of a circular region having a radius C, the exceeded portion is divided into vectors in directions i2, i3 and the vector in the direction i2 is added to the divided vector in the original direction i2. The correctable region exceeding portion of the added vector is divided into vectors in directions i3, i4 and the vector divided in the direction i3 is added to the divided vector of the exceeded vector in the direction i1 divided in the direction i3. By this mechanism, the vector is divided into twoWfour corresponding to the magnitude of the vector and imbalance correction is performed so as to minimize the total corrected amount. On the other hand, divided vector display corrected by the ratio of voltage corresponding to a correctable amount of the vector and voltage corresponding to the vector can be performed.