In a liquid crystal substrate in which a matrix of reflecting electrodes is formed on a substrate, a transistor is formed corresponding to each reflective electrode and a voltage is applied to the reflective electrode through the transistor. The balanced detector system includes at least two optical detectors that receive interference signals. By moving the window and the receivers as a unit a set positional relationship is maintained between all of the elements of the opticsreceiver portion. Furthermore, the collar is embodied in an elastically resilient manner so as to bend in the direction of the piston head when the grooved reinforcement is screwed in, thus prestressing the screwed connection. In this configuration, the developer supply unit comprises a sliding member configured to slide on at least a part of a surface of the holding body moving toward an outside of the developer supply unit through the opening. Moreover, a fin array located along the bottom of the buoy serves as an anti-torque mechanism and improves the operational efficiency of the electricity production.