A current source inverter includes an inverter having arm units and AC terminals, the numbers of the arm units and AC terminals being adapted to an AC load connected to the AC terminals. An upper arm is connected between a positive DC terminal and the corresponding AC terminal and has an upper arm switch Q7 (Q2, Q3) and an upper arm diode. A lower arm is connected between a negative DC terminal 5 and the corresponding AC terminal and has a lower arm switch Q8 (Q5, Q6) and a lower arm diode. The apparatus also includes a smoothing reactor and a DC power source that are connected in series between the positive DC terminal and the negative DC terminal, and includes drivers to control ON/OFF of the upper and lower aim switches to output AC power. The switches Q7 and Q8 are each a normally-ON switch.