An acoustic model training device includes: a processor to execute a program; and a memory to store the program which, when executed by the processor, performs processes of: generating, based on feature vectors obtained by analyzing utterance data items of a plurality of speakers, a training data item of each speaker by subtracting, for each speaker, a mean vector of all the feature vectors of the speaker from each of the feature vectors of the speaker; generating a training data item of all the speakers by subtracting a mean vector of all the feature vectors of all the speakers from each of the feature vectors of all the speakers; and training an acoustic model using the training data item of each speaker and the training data item of all the speakers.