There is provided a radio base station apparatus capable of self-recovery from an AICH abnormal state or notification to maintenance personnel. An RACH preamble detection circuit detects an RACH preamble from an inputted delay profile, and outputs detection information (detection position and reception power) on the detected RACH preamble, to an AICH abnormality determination section. The AICH abnormality determination section determines whether an AICH abnormal state has been caused in which a mobile station retransmits an RACH preamble in spite of a base station having already detected the RACH preamble, based on the detection information. If the AICH abnormal state has been caused, then an AICH/alarm control section controls the transmit power for the AICH or outputs an alarm signal.