Presented are a method and a device for receiving a PPDU in a wireless LAN system. Particularly, a receiving STA receives a PPDU from a transmitting STA through a broadband, 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 of the broadband. The first preamble puncturing pattern includes the pattern in which 40 MHz or 80 MHz band is punctured in the broadband, when the broadband is a 320 MHz band. The first phase rotation value is [1 −1 −1 −1 1 −1 −1 −1 −1 1 1 1 −1 1 1 1].