Abstract: A current source inverter circuit having a plurality of branches, each branch consisting of a pair of thyristors adapted to be switched on alternatingly for power supply from a D. C. power source and diodes connected in series to the thyristors. To each connection point between a thyristor and a diode, there is connected one end of one of a plurality of commutating capacitors, while the other ends of the capacitors are connected in common. An auxiliary charging source is provided between the common connection of the commutating capacitors and one of the terminals of the D. C. source for performing an auxiliary charging for each commutating capacitor through a respective thyristor. Between one of the terminals of the D. C. power source and the common connection of the commutating capacitors, a series circuit consisting of a diode and an auxiliary D. C. source is provided constituting a by-pass for the charging voltage of the commutating capacitor when the associated thyristor is in the ON state.