The application of A.C. motor to servo system is rapidly increased according to the recent advance of power electronics and digital control techniques. The induction motor which has a simple structure and needs less maintenance is used in the industrial field for the variable speed and position control recently. In this paper, the current characteristic of the full-bridge resonant inverter is studied by comparing with the computer simulation and the laboratory experiment when the ratio of forced frequency to the natural frequency and the ratio of conduction time to the period at the given frequency is changed. And then, the full-bridge resonant inverter is applied to the speed control of single phase induction motor.