Provided are a method for a user equipment to select a codebook index in a wireless communication system and an apparatus supporting the method. The method performed by the user equipment comprises performing zero padding for a first vector, wherein the first vector represents a channel state measured by a receive antenna for a first transmit antenna; performing IFFT for a second vector, wherein the second vector is obtained by performing the zero padding for the first vector; performing receive antenna combining for a third vector, wherein the third vector is obtained by performing IFFT for the second vector; and detecting a maximum element from a fourth vector, wherein the fourth vector is obtained by performing the receive antenna combining for the third vector.