An LPF performs low-pass filtering for a light reception signal responsive to return light received by an optical pickup. A comparator makes a comparison between the level of the signal output from the LPF and a predetermined threshold value and outputs a high or low pulse signal MIR. A system control section determines the pulse signal MIR for each predetermined dot region. If the pulse signal MIR output from the comparator is high, the system control section writes “1” into buffer memory; if the pulse signal MIR is low, the system control section writes “0” into the buffer memory. The pixel string data recorded in the buffer memory is transferred to a host and an image responsive to pixel string data is displayed on a display.