A radio base station device comprises: a preamble signal receiving unit (15) that receives a RACH preamble signal transmitted from a radio terminal device; a reception notice receiving unit (16) that receives, from a radio relay station device, a reception notice indicating that the radio relay station device has received the RACH preamble signal; and a response signal transmitting unit (18) which, when an identifier (RA-ID) of the RACH preamble signal transmitted from the radio terminal device matches an identifier comprised in the preamble reception notice transmitted from the radio relay station device, permits the use of an identifier by the radio relay station device and transmits, to the radio terminal device, a RACH response signal (RACH Response) comprising a cell identifier (Cell ID) of a cell managed by the radio relay station device permitted to use the identifier. Accordingly, the latency when establishing a connection can be reduced.