1. A method for improving an acoustic model, comprising: acquiring, by a computer, a first standard deviation value by calculating standard deviation of a feature from first training data; acquiring, by the computer, a second standard deviation value by calculating standard deviation of a feature from second training data acquired in a different environment from an environment of the first training data, wherein the amount of the first training data is smaller than the amount of the second training data, and wherein environment includes the recording hardware and software used to acquire training data; creating, by the computer, 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 reconstructing, by the computer, 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.