One embodiment of the present invention is a method for user equipment transmitting a physical sidelink shared channel (PSSCH) in a wireless communication system, the method for transmitting a PSSCH comprising the steps of: performing sensing on an m number of subframes indicated by upper layer signaling from among an n number of subframes in a sensing window; repeating sensing of the m number of subframes at an interval of the n number of subframes within the sensing window; selecting, as a transmission resource, the m number of subframes from among the n number of subframes within a selection window, on the basis of the result of sensing the m number of subframes; and transmitting the PSSCH through the m number of subframes selected as the transmission resource.