A transmitting multi-link device (MLD) in a wireless local area network system enables a first station (STA) to perform a back-off operation again without transmitting PPDU, if a second STA is in the middle of receiving even when a back-off counter (BC) of the first STA becomes 0. The first STA and the second STA are included in the same transmitting MLD. The first STA operates on a first link and the second STA operates on a second link. The first and second links are included in a non-simultaneous transmit and receive (NSTR) link pair.