PURPOSE: To generate AC voltage having a small amount of distortion and high efficiency by a simple constitution by successively changing over batteries for a DC power supply consisting of a plurality of batteries connected in series.

CONSTITUTION: Contacts 41, 51 for changeover switch means 4, 5 are connected selectively, a changeover control means 3 successively changes over each contact for a changeover means 2 to 20, 21,..., 2n, and output voltage is increased in the forward direction while using a line L2 as a reference. Each contact for the changeover means 2 is changed over to 2n,..., 21, 20 in succession, and output voltage is reduced as positive values and to zero. Each contact 42, 52 for the changeover switch means 4, 5 is connected selectively at that time, and polarity is inverted. The contacts of the changeover means 2 are changed over to 20, 21,..., 2n, thus increasing output voltage in the negative direction. The contacts are changed over to 2n,..., 21, 20, thus lowering output voltage as negative values and to zero. The output is extracted from output terminals 81, 82 through contacts 71, 70 for a changeover switch, thus acquiring AC voltage.