PURPOSE: To easily convert the frequency of AC power by respectively connecting each output terminal of an AC power source to the input terminal of an AC load through switching elements and controlling the ignition of the switching elements in accordance with the required operating state of the AC load by means of a control circuit.

CONSTITUTION: A frequency converter for AC power is provided with thyristors A1-D2 which connect a single-phase DC power source to an AC load 10 and a control circuit 4 which controls the ignition of the thyristors A1-D2. When the ignition of thyristors A1, A2, D1, and D2 is controlled, AC power from an AC power source is supplied to the load 10 without converting the frequency (f) of the power. When the ignition of thyristors B1 and C1 is alternately controlled, a half-wave component is supplied to the load 10 and converted into AC power having a frequency corresponding to f/2. When the control circuit 4b of a converter 1b controls the ignition of the thyristors A1-D2, the speed of an induction motor 2 can be switched between the full speed and a half full speed. Thus, the frequency of AC power can be converted easily.