The power dissipation in radio-frequency discharges of Ar, O-2, and SF6 gases was measured from the voltage and current waveforms with a parallel-plate-type reactor. A circuit constructed with coils and condensers was connected parallel to the electrodes in order to reduce the current flowing outside the discharges. In some experiments, a displacement current through the discharge was canceled in order to obtain an accurate value of the power dissipation. The power efficiency was between 0.3 and 0.8. The power loss outside the discharge was related to the discharge impedance. The relation between the power efficiency and the discharge impedance was obtained with a simple equivalent circuit. In the equivalent circuit, the parasitic resistance which shows the power loss outside the discharge was assumed to be connected parallel to the discharge impedance. The resistance was almost constant under various discharge conditions in our experiments.