This paper deals with the design of an electrical model for the photovoltaic effect in a PLZT element to estimate, in advance, the performance of an optical actuator consisting of PLZT elements. The results of the basic experiment on the photovoltaic effect are shown, and they indicate that a parallel circuit including a current source, a resistance and a capacitance may be applicable to an electrical model for the photovoltaic effect, under the consideration of the lumped system. Then, the step response of the photovoltage is obtained theoretically according to the electrical model proposed. Since the theoretical results agree well with the results of the basic experiment, the electrical model proposed can be considered to be valid for practical use. Important aspects of the design of an exact model are also pointed out.