An object of the present invention is to provide a terminal device, a communication method, and a communication system which are capable of reducing the error rate even if the transmitting side and the receiving side are asynchronous. The terminal device, communication method, and communication system according to the present invention sample an optical signal more finely than a 0/1 bit pattern in optical ID estimation processing for determining which of 1/0 the data acquired by an optical sensor is, and perform a majority decision using a plurality of sampling values in a decision processing window. Thus, even if the correct sampling value fails to be obtained, the correct bit value can be derived from other samplings.