1. A computer for improving an acoustic model, comprising: a standard deviation value calculating unit for calculating standard deviation of a feature from first training data to acquire a first standard deviation value and calculating standard deviation of a feature from second training data acquired in a different environment from an environment of the first training data to acquire a second standard deviation value, wherein the amount of the first training data is smaller than the amount of the second training data; a feature creating unit for creating a feature adapted to an environment where the first training data is recorded, by multiplying the feature acquired from the second training data by a ratio obtained by dividing the first standard deviation value by the second standard deviation value; and an acoustic model reconstructing unit for reconstructing an acoustic model constructed using training data acquired in the same environment as the environment of the first training data, using the feature adapted to the environment where the first training data is recorded.