Provided is a method for a first device to perform sidelink communication with a second device. The method comprises: determining a first resource for a first sidelink transmission; receiving, from a third device, a SCI including information related to a second resource for a second sidelink transmission; determining to reselect the first resource, based on overlap of the first resource and the second resource and a relationship between a first priority value of the first sidelink transmission and a second priority value of the second sidelink transmission satisfying a pre-configured condition; and transmitting, to the second device, a first PSCCH related to the first sidelink transmission or a first PSSCH related to the first PSCCH, based on a third resource determined by reselecting the first resource, wherein the pre-configured condition includes a condition in which the first priority value is greater than the second priority value.