A apparatus includes: a storage unit to store a model representing a relationship between a relative time and an occurrence probabilities; a first detection unit to detect first speech period of a first speaker; a second period detection unit to detect second speech period of a second speaker; a unit to calculate a feature value of the first speech period; a detection unit to detect a word using the calculated feature value; an adjustment unit to make an adjustment such that in detecting a word for a reply by the detection unit, the adjustment unit retrieves an occurrence probability corresponding to a relative position of the reply in the second speech period, and adjusts a word score or a detection threshold value for the reply; and a second detection unit to re-detect, using the adjusted word score or the adjusted detection threshold value, the detected word by the detection unit.