According to one embodiment of the present disclosure, provided is a method by which a first device performs sidelink communication with a second device. The method can comprise the steps of: determining a first resource for first sidelink transmission; receiving, from the second device or a third device, on an Nth slot, SCI including information related to a second resource for second sidelink transmission; determining, on the basis of a DMRS RSRP threshold value and a DMRS RSRP measurement value of a first PSCCH related to the SCI, whether to reselect the first resource overlapping with the second resource on an N+Kth slot spaced from the Nth slot by K slot length; and transmitting, to the second device, a second PSCCH related to the first sidelink transmission or a PSSCH related to the second PSCCH, on the basis of the determination on whether to reselect.