A sheet separating device includes a stacker, a pickup member, an air supplier, and a sheet floating restraint. The stacker is configured to stack a plurality of sheets. The pickup member is configured to convey the plurality of sheets one by one from the stacker. The air supplier includes an air outlet, at a downstream side of the stacker in a sheet conveyance direction. The air supplier is configured to blow air toward a downstream end of the plurality of sheets in the sheet conveyance direction. The sheet floating restraint is configured to restrict floating of a part of the plurality of sheets separated by air blown from the air outlet. The sheet floating restraint is replaceable with another sheet floating restraint. The sheet floating restraint and said another sheet floating restraint have respective shapes different from each other.