To provide a liquid ejection device for which bending that occurs in a width direction orthogonal to the transport direction of an ejection medium that is supported by suction on a medium support unit is made uniform.

A liquid ejection device includes: a transport unit for transporting a paper RP3; a medium support unit 20 including a medium support surface SM on which the transported paper is supported by suction with negative pressure; and a liquid ejection head for ejecting ink to the paper supported on the medium support unit. On the medium support surface of the medium support unit, first recesses H1 to H18 and second recesses F0 to F3 are arranged side by side along a width direction, wherein, the first recesses H1 to H18 are imparted with negative pressure, and each recess of which is formed so that a width dimension of an opening in the width direction orthogonal to the transport direction of an ejection medium becomes larger on a downstream side than on an upstream side of the transport direction and the second recesses F0 to F3 are imparted with negative pressure, and each recess of which is formed so that a width dimension of an opening in the width direction becomes smaller than the width dimension on the downstream side of the transport direction of the first recess. The second recesses are configured to accept the liquid ejected toward the ejection medium from the liquid ejection head.