Abstract: A highly efficient high voltage generating device comprises a switching circuit 2 comprising plural switching elements S1˜S4 and connected with a direct current power source circuit 1, a rectifying circuit 4, a primary winding N1 connected with the switching circuit 2, a secondary winding N2 connected with the rectifying circuit 4 and a control circuit 5 to control the switching circuit 2. The control device 5 is configured to perform a current circulation function of passing a current to circulate between the switching circuit 2 and the transformer 3 to reverse polarity of a voltage VCp2 over the secondary winding N2, while keeping on at least one of the switching elements S1˜S4.