1. A method of training a language model, the method comprising: converting, using a processor, training data into error-containing training data; and training a neural network language model using the error-containing training data wherein the converting comprises selecting a word to be replaced with an erroneous word from words in the training data, and generating the error-containing training data by replacing the selected word with the erroneous word, wherein the neural network language model is used to estimate a connection relationship between words, wherein the selecting comprises randomly selecting the word from the words in the training data, wherein the processor is configured to use the trained language model to convert a speech into output data.