The present invention relates to a wireless communication system, and specifically, to: a method comprising a step in which first PDCCH monitoring is performed in a first SS set group within a cell group configured for an SS set group switching operation, and a step in which, from a 1st slot coming at least P symbols after a reference time, the first PDCCH monitoring is stopped in the first SS set group and second PDCCH monitoring is started in a second SS set group for cells in the cell group, wherein the numerology of the P symbols is determined as a cell group-common value on the basis of the smallest SCS among a plurality of SCSs on the basis of the plurality of SCSs being configured for the cell group; and an apparatus for same.