A medium flattening method, when a medium is transported by being adhered to an adhesive layer which is on a surface of a transport belt, includes detecting a presence or absence of floating being generated in the medium on the transport belt using a sensor, executing a process for flattening to flatten the floating in the medium in the case where the floating exists, and transporting the medium, where the floating is eliminated using the process for the flattening, to a liquid discharge region of a liquid discharge section.