An optical signal receiving equipment including an optical-electrical converter configured to convert optical signals into electronic signals; first deciders configured to transform the electronic signals into first binary signals; a second decider configured to transform the electronic signals into a second binary signal; a decision encoder configured to compute identification signals based on the plurality of first binary signals, and to compute reliability information of the computed identification signals; a converter configured to combine the identification signals and the second binary signal to combined identification signals; and a controller configured to execute an initial identification of the electronic signals in any one of the plurality of first deciders by using an initial threshold level in the plurality of first deciders, to measure an average amplitude of the electronic signals, and to correct the threshold level of the plurality of first deciders based on a variation of the average amplitude of the electronic signals.