1. An information reproducing apparatus for detecting data recorded in a medium by Partial Response and Maximum Likelihood signal processing units and an equalizer, the apparatus comprising: a table which stores plural pairs of a true pattern and a false pattern; a pattern comparator which compares the detected data with the true patterns and the false patterns stored in the table to find a pair of the true pattern and the false pattern one of which pattern coincides with the detected data; and a calculating device which, when the pattern comparator finds the pair, calculates: a first Euclidean distance (E 2 F,S ) between an output signal of the equalizer and an ideal signal of the false pattern included in the pair, a second Euclidean distance (E 2 T,S ) between an output signal of the equalizer and an ideal signal of the true pattern included in the pair, a difference between the first Euclidean distance and the second Euclidean distance, and an average (μ) and a standard deviation (σ) of a distribution of the difference, wherein the detected data is evaluated based on the average (μ), the standard deviation (σ), and F ⁡ ( 0 ) = ∫ - ∞ 0 ⁢ exp ⁢ { - ( x - μ ) 2 / 2 ⁢ σ 2 } σ ⁢ 2 ⁢ π ⁢ ⁢ ⅆ x