A medium support unit of a liquid ejection device has a negative pressure chamber and a medium support surface so that an ejection medium is supported on the medium support surface by suction, and includes a plurality of first recesses and at least one second recess. The first recesses are in communication with a negative pressure generating unit, and aligned along a width direction. The second recess is disposed at a position corresponding to an end part in the width direction of the ejection medium, and arranged to accept liquid ejected from a liquid ejection head. The second recess is in communication with an adjacent one of the first recesses at a position inward of the end part of the ejection medium. The first recesses are respectively in communication with the negative pressure generating unit via the negative pressure chamber partitioned into a plurality of units in the width direction.