A liquid ejection device includes a liquid ejection head including a surface formed with nozzles arranged in a first direction, a head moving unit reciprocating the liquid ejection head along a line parallel to the surface and perpendicular to the first direction, a conveyor portion conveying the recording medium in the first direction, and a corrugate mechanism disposed upstream or downstream of the liquid ejection head in the first direction and forming the recording medium in a predetermined corrugated shape. A controller determines an ejection timing for ejecting liquid from ones of the nozzles appropriate to a corrugated shape formed in the recording medium while the liquid ejection head is moved, a memory that stores ejection timing information, and a gap sensor that moves with the liquid ejection head to determine a gap between the recording medium and the liquid ejection surface in the second direction.