1. A method for generating a record sentence to establish a speech corpus, comprising: generating a synthesized sentence of speech and synthesis information related to speech synthesis by performing speech synthesis for a predetermined sentence of text; selecting an unseen sentence including an unseen unit according to the synthesis information; generating a weight indicating a recording priority of the unseen unit included in the selected unseen sentence; and generating a record sentence by combining the unseen unit with the speech synthesis information according to the generated weight.