Setting an electrically controllable dual focal-point (DFP) lens into the optical resonator of a laser, we can readily modulate the output power of the optical beam with a relatively low voltage. The DFP lens is fabricated by combining an electro-optic (E-O) material with the Fresnel zone-plate (FZP) lens, in which numerous transparent (ITO) electrodes are evaporated in the form of the Fresnel zone- plate (FZP) on a PLZT ceramic E-O plate to compose a dual focal-point lens with and without an applied voltage. In addition, the PLZT (La/Zr/Ti equals 9/65/35) ceramic used here as an E-O material represents a quadratic E-O effect. Inserting this DFP E-O lens inside the optical resonator of an He-Ne 3.39 mm laser on trial, the fundamental modulation characteristics are investigated. As a result, about 15.5% modulation degree was obtained with applying the rf (2 kHz) voltage of 13.5 Vp under a certain bias. The operational principle is experimentally demonstrated together with theoretical discussions.