Disclosed are a method and a device for allocating resource units using leftover tones in a wireless LAN. The method for allocating resource units using leftover tones in a wireless LAN may comprise the steps of: an AP generating PPDUs to be transmitted to a plurality of STAs; and the AP transmitting the PPDUs to the plurality of STAs on all frequency bands, wherein the PPDUs are transmitted from each of a plurality of resource unit sets respectively allocated to each of the plurality of STAs, wherein each of the plurality of resource unit sets includes a first resource unit set and a second resource unit set, wherein the first resource unit set includes at least one resource unit, the second resource unit set includes one tone design resource unit, and wherein the tone design resource unit may include at least one other resource unit and at least one additional tone unit.