A radio base station apparatus for transmitting signals to a plurality of user equipments using a downlink shared channel (HS-PDSCH) shared by the plurality of user equipments and receiving signals from each user equipment via an uplink channel, comprising: a plurality of antenna elements (1a - 1n) for transmitting and receiving radio signals; a detection unit (24a - 24n) for detecting information about an uplink channel corresponding to a first user equipment from signals received via said plurality of antenna elements; a directivity control unit for determining directivity of transmission power based on the information detected by said detection unit when signals are transmitted to the first user equipment via the downlink shared channel (HS-PDSCH); and a transmission unit for transmitting signals with the directivity determined by said directivity control unit; characterised in that said uplink channel is an uplink dedicated channel (DPDCH); and in that the radio base station apparatus further comprises a channel selection unit for selecting, based on traffic volume of transmission data to a user equipment, a downlink dedicated channel (DPDCH) or the downlink shared channel(HS-PDSCH) as a communication channel for transmitting a signal to the user equipment, wherein while data is transmitted to the user equipment via the downlink shared channel (HS-PDSCH), the directivity is calculated based on the information detected in a high speed dedicated control channel (HS-PDCCH), and while data is not transmitted to the user equipment via the downlink shared channel(HS-PDSCH), the directivity is calculated based on the information detected in a dedicated control channel (DPCCH); and when a communication channel for transmitting a signal to the first user equipment is changed from the downlink dedicated channel (DPDCH) to the downlink shared channel (HS-PDSCH) by said channel selection unit, said directivity control unit determines directivity of a transmission beam for transmitting a signal via the downlink shared channel (HS-PDSCH) according to lastly detected reception power of an uplink channel (DPCCH) corresponding to the downlink dedicated channel (DPDCH) before the channel switching, until reception power of an uplink channel (HS-DPCCH) corresponding to the downlink shared channel (HS-PDSCH) after the channel switching is obtained by said detection unit (24a - 24n), and said directivity control unit determines directivity of the transmission beam for transmitting a signal via the downlink shared channel (HS-PDSCH) according to detected reception power of the uplink channel (HS-DPCCH) corresponding to the downlink shared channel (HS-PDSCH) after the reception power of the uplink channel (HS-PDCCH) corresponding to the downlink shared channel (HS-PDSCH) is detected. a plurality of antenna elements (1a - 1n) for transmitting and receiving radio signals; a detection unit (24a - 24n) for detecting information about an uplink channel corresponding to a first user equipment from signals received via said plurality of antenna elements; a directivity control unit for determining directivity of transmission power based on the information detected by said detection unit when signals are transmitted to the first user equipment via the downlink shared channel (HS-PDSCH); and a transmission unit for transmitting signals with the directivity determined by said directivity control unit; characterised in that said uplink channel is an uplink dedicated channel (DPDCH); and in that the radio base station apparatus further comprises a channel selection unit for selecting, based on traffic volume of transmission data to a user equipment, a downlink dedicated channel (DPDCH) or the downlink shared channel(HS-PDSCH) as a communication channel for transmitting a signal to the user equipment, wherein while data is transmitted to the user equipment via the downlink shared channel (HS-PDSCH), the directivity is calculated based on the information detected in a high speed dedicated control channel (HS-PDCCH), and while data is not transmitted to the user equipment via the downlink shared channel(HS-PDSCH), the directivity is calculated based on the information detected in a dedicated control channel (DPCCH); and when a communication channel for transmitting a signal to the first user equipment is changed from the downlink dedicated channel (DPDCH) to the downlink shared channel (HS-PDSCH) by said channel selection unit, said directivity control unit determines directivity of a transmission beam for transmitting a signal via the downlink shared channel (HS-PDSCH) according to lastly detected reception power of an uplink channel (DPCCH) corresponding to the downlink dedicated channel (DPDCH) before the channel switching, until reception power of an uplink channel (HS-DPCCH) corresponding to the downlink shared channel (HS-PDSCH) after the channel switching is obtained by said detection unit (24a - 24n), and said directivity control unit determines directivity of the transmission beam for transmitting a signal via the downlink shared channel (HS-PDSCH) according to detected reception power of the uplink channel (HS-DPCCH) corresponding to the downlink shared channel (HS-PDSCH) after the reception power of the uplink channel (HS-PDCCH) corresponding to the downlink shared channel (HS-PDSCH) is detected.