1. A data processing apparatus comprising: a branch-metric computation section configured to compute a branch metric while limiting the number of child states each originated from a parent state in a trellis used for inferring a data series to a number M determined in advance; a state-metric computation section configured to compute a state metric of a candidate for a surviving state surviving in said trellis by making use of said branch metric; a detection section configured to detect a minimum state metric which is a smallest state metric among state metrics each computed as a candidate for a surviving state; a storage section configured to store states, which have been each originated through branches in said trellis from an effective state reached by going upstream from a state with said minimum state metric through said branches in said trellis by a distance of (L−1) time units where L is a cutoff length used as a unit for cutting off a process to infer said data series, as surviving states; and a selection section configured to select a candidate, which corresponds to said effective state to serve as a candidate for data composing said data series, to be used to serve as a candidate for the inferred value of said data.