A sheet stacker includes a sheet ejector, a sheet stack portion, and air blowers. The sheet ejector ejects a sheet. The sheet stack portion stacks the sheet ejected by the sheet ejector. The air blowers blow air from blow ports toward the sheet ejected from the sheet ejector. Each of the air blowers includes an air generator, an air guide, a first blow portion, a second blow portion, and a switcher. The air generator generates the air. The air guide guides the air to each of the blow ports. The first blow portion blows the air toward the sheet. The second blow portion blows the air in a direction different from a direction in which the first blow portion blows the air. The switcher performs switching so that the air guide guides the air to one of the first blow portion and the second blow portion.