A parallel-to-serial conversion circuit may include first to fourth data lines; first to fourth parallel-to-serial converters configured to parallel-to-serial convert data of corresponding two data lines, among the first to fourth data lines, at a ratio of 2:1, respectively; and first to fourth drivers configured to transmit converted data of corresponding parallel-to-serial converter, among the first to fourth parallel-to-serial converters, respectively, to an output line, wherein two of the first to fourth drivers are simultaneously activated.