In a Wireless Local Area Network system, an STA may receive a trigger frame from an AP. The trigger frame may include a common information field and user information fields. Each of the user information fields may include a first field related to an association identifier (AID) and a second field including information for the STA related to the AID. The second field may include special information for every STA receiving the trigger frame on the basis that the first field has a specific value. The common information field may include a present field related to whether a user information field in which the first field has the specific value is present among the user information fields.