A method for allocating a physical hybrid ARQ indicator channel (PHICH) is discussed. The method includes allocating a CDM group according to a cyclic prefix type in consideration of a ratio of the numbers of necessary CDM groups according to spreading factors, and allocating a PHICH to the allocated CDM group. The PHICH includes an ACK/NACK signal multiplexed by code division multiplexing (CDM). Therefore, resources for PHICH transmission are efficiently allocated and a transmission structure can be maintained irrespective of a spreading factor.