Abstract: In a gate driver device, cathode conductor 2, gate conductor 3, and positive and negative conductors 8 and 9 between the principal turn-on and turn-off capacitors and MOSFET switching elements Q11-Q1i and Q21-Q2j are disposed on a wide plate. A thin insulation layer is inserted between conductor 3 and conductors 8 and 9. Numerous chip-type ceramic capacitors C11-C1m and C21-C2n to be used as principal capacitors are arranged in rows in the space between conductor 2 and conductors 8 and 9. The gate voltage of switching elements Q11-Q1i is reduced exponentially by time constant circuit TC, and the leak inductance of transformer Thf is employed to smooth the charging current.