The readout characteristics of the partial response (PR) channel of an magneto-optical disk system is presented. The PR class 11 or its modification PR(1,u,1) channel, is found to be favorable in detecting data from MO channel in which the minimum mark size is about 30% of the diameter of readout optical spot. The dual-level independent edge-detection (DLE) method is newly developed for reproducing method instead of a simple threshold-detection method, with considering fluctuations of media and head. The DLE method has a 2.5-dB advantage in SNR compared with the simple threshold-detection. Assuming a 20-dB SNR, the window margin with 10^4 samples is more than fifty percent of the window.