Disclosed is a method for a first terminal determining a transmission beam in a wireless communication system supporting a sidelink. Specifically, the method may comprise: receiving beam-associated information from a second terminal; and on the basis of the beam-associated information, determining a transmission beam for the second terminal. Particularly, the beam-associated information may include: a beam index; and a time resource index for the beam index. The UE is capable of communicating with at least one of another UE, a UE related to an autonomous driving vehicle, a base station or a network.