Presented are a method by which a multi-RU receives a LDPC-tone-mapped PPDU in a wireless LAN system, and an apparatus. Particularly, a reception STA receives, from a transmission STA, a PPDU including a data field and decodes the data field. The data field is received through the multi-RU. LDPC tone mapping for data tone included in the data field is performed on the basis of a first parameter with respect to the multi-RU. The first parameter is 18 when the multi-RU is an RU in which the 242 tone RU and the 484 tone RU are aggregated.