1. A speech recognition apparatus comprising: a generating unit configured to generate a speech feature vector expressing a speech feature for each of a plurality of frames obtained by dividing an input speech between a start time and an end time and including frames from a start frame to an end frame; a first storage unit configured to store a first acoustic model obtained by modeling a speech feature of each word by using a state transition model including a plurality of states and a plurality of transition paths, each word being included in the input speech; a second storage unit configured to store at least one second acoustic model different from the first acoustic model; a first calculation unit configured to calculate, for each state, a first probability of transition to a state at the end frame for each word from the first acoustic model and a speech feature vector sequence from the start frame to the end frame to obtain a plurality of first probabilities for each word, and select a maximum probability of the first probabilities; a selection unit configured to select, for each word, a maximum probability transition path corresponding to the maximum probability, the maximum probability transition path indicating transition from a start state at the start frame to an end state at the end frame; a conversion unit configured to convert, for each word, the maximum probability transition path into a corresponding transition path corresponding to the second acoustic model; a second calculation unit configured to calculate, for each word, a second probability of transition to the state at the end frame on the corresponding transition path from the second acoustic model and the speech feature vector sequence; and a finding unit configured to find to which word the input speech corresponds based on the maximum probability for each word and the second probability for each word.