Method and apparatus for changing operating mode in wireless lan system

Disclosed is a signal processing method for changing an operating mode for transmitting a PPDU in a wireless LAN system. Specifically, a first station transmits, to a second station, the number of spatial streams supported by the first station, and a first instructional information instructing a change of the operating mode indicating a channel bandwidth. The first station applies the first instructional information after receiving an ACK therefor. The first instructional information comprises an operating mode indicator for indicating whether the operating mode is a receive operating mode (ROM) or a transmit operating mode (TOM).