A multi-channel array transducer can enlarge the treatment volume of HIFU (High-Intensity Focused Ultrasound), which is a noninvasive method for cancer therapy, by generating and scanning multiple foci. In our previous study, we developed a compact and highly efficient driving circuit using staircase wave voltage for typical single HIFU transducer that the impedance is almost real at the resonance frequency. However, an array transducer element can have too capacitive impedance that affects the output voltage waveform designed for reducing the harmonics components. To solve this problem, we propose a new circuit to drive an array transducer considering its imaginary impedance. The proposed circuit was able to reduce not only the odd harmonics but also electrical power consumption. Simulation of the relationship between the number of staircase wave steps and the power consumption proved that the total power consumption due to intentional turn-on decreased in proportion to the number of steps.