The present invention provides a method for performing an initial access process used in a wireless access system and in an ultrahigh frequency band, and devices supporting same. The method for performing a high-speed initial access process in a wireless access system supporting an ultrahigh frequency band, according to one embodiment of the present invention, may comprise the steps of: receiving a synchronizing signal; receiving a broadcast channel signal; generating a random access preamble by using pre-fixed physical random access parameters according to a small cell supported in the ultrahigh frequency band; and transmitting the generated random access preamble on the basis of the synchronizing signal and the broadcast channel signal.