A user apparatus in a radio communication system including a base station and the user apparatus, including: a reception unit configured to receive a plurality of predetermined signals transmitted from the base station by a plurality of beams; and a transmission unit configured to transmit a preamble using a resource corresponding to at least one beam of the plurality of beams, wherein the reception unit measures a reception quality for each of the plurality of beams, and the transmission unit transmits the preamble using a resource corresponding to a beam of a reception quality that satisfies a predetermined condition.