Disclosed are a method and an apparatus for generating an STF signal usable in a wireless LAN system. The STF signal is included in a field used to improve AGC estimation of a MIMO transmission. A portion of the STF signal is used to transmit an uplink, and can be used for uplink MU PPDUs transmitted from a plurality of STAs. The STF that is suggested, for example, is used for a 40 MHz band or an 80 MHz band and can be generated based on a sequence in which a predetermined M sequence is repeated. The predetermined M sequence can be a binary sequence of which the length is 15 bits.