1. A speech translation system comprising: a first terminal device comprising a first speech input for inputting a first speech of a first language spoken by a first user, and converting the first speech to a first speech signal; a second terminal device comprising a second speech input for inputting a second speech of a second language spoken by a second user, and converting the second speech to a second speech signal; a speech recognition device that receives the first speech signal and the second speech signal, recognizes the first speech signal to a first recognized text, and recognizes the second speech signal to a second recognized text; a machine translation device that receives the first recognized text and the second recognized text, translates the first recognized text to a first translated text of the second language, and translates the second recognized text to a second translated text of the first language; a control device; wherein the first terminal device receives (a) a first text set of the first language being the first recognized text and the second translated text, and (b) a second text set of the second language being the second recognized text and the first translated text, and comprises a first display unit that displays the first text set and the second text set; and the second terminal device receives at least one text of the second text set, and comprises a second display unit that displays the at least one text of the second text set; a third terminal device comprising a third speech input for inputting a third speech of a third language spoken by a third user, and converting the third speech to a third speech signal; the speech recognition device receives the third speech signal, and recognizes the third speech signal to a third recognized text; the machine translation device receives the third recognized text and the first recognized text, further comprises a third machine translation unit that translates the third recognized text to the third translated text of the first language, and translates the first recognized text to the fourth translated text of the third language; the first display unit displays (a) at least one text set of the second text set and a third text set of the third language being the third recognized text and the fourth translated text, and (b) the fourth text set of the first language being the first text set and the third translated text; and the third terminal device further comprises the third display unit that displays at least one text of the third text set.