The droplet ejector includes: a head unit set composed of four head units arranged in a staggered manner in the arrangement direction; a head supporting member which supports the head unit set; a liquid supplier which supplies liquid to the head unit set; and a conveyor mechanism which conveys an ejection target. Each head unit has a passage structure having a liquid passage. At one edge of the passage structure in the arrangement direction, a liquid supply opening which is connected to the liquid passage and the liquid supplier is provided. Two passage structures neighboring in the arrangement direction are disposed so that the respective edges where the liquid supply openings are provided oppose each other in the arrangement direction.