The present document relates to a wireless communication system and, more particularly, to a method for performing retransmission in a wireless LAN system to which transmission opportunity (TXOP) sharing is applied, and a device therefor. To this end, a station transmits an initial transmission frame including primary access category (AC) information and secondary access category (AC) information; and when there is no response to the secondary AC information of the initial transmission frame, reconfigures a back-off timer value for the secondary AC information and retransmits the secondary AC information according to the reconfigured back-off timer value.