A machine translation method is provided, in which a plurality of different forward-translated sentences is generated resulting from translation of a received translation-source sentence in a first language into a second language. A plurality of backward-translated sentences is generated resulting from backward translation of the plurality of different forward-translated sentences into the first language. As translation-source sentence, voice information or text information is received. The voice information is received via a microphone that receives a voice input performed by a user. The text information is received via a text input device that receives a text input performed by a user. An output form of the forward-translated sentence corresponding to the selected backward-translated sentence is changed in accordance with which of the voice information and the text information is received as the translation-source sentence.