Proposed are a method and a device for transmitting and receiving important update information of another AP through an ML element in a WLAN system. Specifically, a receiving MLD receives a basic ML element from a transmitting MLD over a first link. The receiving MLD decodes the basic ML element. The basic ML element includes a profile field of the second transmitting STA. The profile field of the second transmitting STA includes a first CSF presence field. When the value of the first CSF presence field is set to 0, the profile field of the second transmitting STA includes a first CSF field. The first CSF field includes information about the current change sequence number of the second transmitting STA.