A light transmittance adjusting apparatus for adjusting a windowpane of an automobile or a building has a fixed member and a movable member arranged in parallel with each other and having a plurality of light interception sections and light transmission sections formed thereon alternately. The vertical position of the movable member are changed electrostatically relative to the fixed member to adjust the light transmittance of the windowpane. Each light interception section has a semi-interception region, the light transmittance of which decreases gradually from a center region thereof toward the adjacent light transmission section. The semi-interception region of the light interception section of a light interception plate of the fixed member overlap the semi-interception region of the light interception section of a light interception plate of the movable member, thus accomplishing an optical interception completely.