Proposed are a method and device for receiving a PPDU in a wireless LAN system. Specifically, a reception STA receives the PPDU from a transmission STA through a wide band, and decodes the PPDU. The PPDU includes a legacy preamble, and first and second signal fields. The legacy preamble and the first and second signal fields are generated on the basis of a first phase rotation value. The first phase rotation value is acquired on the basis of a first preamble puncturing pattern in a wide band. When the wide band is a 240 MHz band, the first preamble puncturing pattern includes a pattern in which a 40 MHz or 80 MHz band in the wide band is punctured. The first phase rotation value is [1 1 −1 1 −1 1 −1 −1 −1 −1 1 1].