A parallel to serial conversion circuit makes output data normally swing even in a high-speed operation. The parallel to serial conversion circuit includes a main selection block configured to drive an output node sequentially in response to data on a first line and data on a second line, and a subsequent selection block configured to drive the output node sequentially in response to data on a subsequent first line and data on a subsequent second line, wherein the output node is driven by inverted data of the data on the subsequent first line and inverted data of the data on the subsequent second line.