A liquid crystal display apparatus to which the present invention is applied has a first data conversion circuit and a second data conversion circuit. A method for estimating the parking occupancy within the area of interest can include the use of vehicle entry and exit data from the area of interest, as well as an estimated transit time for vehicles transiting through the area of interest without parking. , a gain of an amplifier circuit by which a read signal read from the magnetic disk is amplified to a predetermined output, determines a rewrite sector count based on the amplification degree, and performs data rewriting according to the rewrite sector count. The polyphase filter receives the input current signals and generates four output current signals that are out of phase with each other.