A method for transmitting a physical protocol data unit (PPDU) of a station (STA) device in a wireless local area network (WLAN) system, includes generating a PPDU configured based on a high efficiency-short training field (HE-STF) sequence including a HE-STF field and transmitting the PPDU, wherein the HE-STF field is transmitted on a channel, wherein the HE-STF sequence is mapped to the channel per 2-tone unit, wherein, when the channel is a 20 MHz channel, the HE-STF sequence is configured to have a structure of {a M Sequence, 0, 0, 0, 0, 0, 0, 0, the M sequence}, and, when the channel is a 40 MHz channel, the HE-STF sequence is configured to have a structure of {the M sequence, 0, 0, 0, 1, 0, 0, 0, the M sequence, 0, 0, 0, 0, 0, 0, 0, the M sequence, 0, 0, 0, 1, 0, 0, 0, the M sequence}.