A base station apparatus for receiving an uplink shared channel (PUSCH, UL-SCH) from a user apparatus and informing the user apparatus whether the user apparatus has to retransmit the uplink shared channel (PUSCH, UL-SCH), comprising: i) a transmit power control unit configured to determine transmit power for a HARQ indicator channel (PHICH) indicating a positive response or a negative response to the uplink shared channel (PUSCH, UL-SCH); and ii) a transmitting unit configured to transmit a transmission signal to the user apparatus, the transmission signal including the HARQ indicator channel (PHICH) at the transmit power determined by the transmit power control unit, iii) wherein different transmit power for the HARQ indicator channel (PHICH) is set depending on (a) whether the transmission signal includes a control channel (UL-grant) for allowing the uplink shared channel (PUSCH, UL-SCH) to be transmitted or (b) whether the transmission signal includes the HARQ indicator channel (PHICH) indicative of the positive response; wherein i-1) the transmit power control unit is further configured to calculate the transmit power Power for the HARQ indicator channel (PHICH) in accordance with Power = Power Ref + CQI Ref − CQI + Δ, where Power Ref represents reference transmit power, CQI Ref represents reference radio quality information, CQI represents the downlink radio quality information, and Δ represents an offset, wherein the offset Δ is set to different values for the following four cases: 1) a case where the HARQ indicator channel (PHICH) indicative of the positive response is transmitted but the control channel (UL-grant) for allowing the uplink shared channel (PUSCH, UL-SCH) to be transmitted is not transmitted; 2) a case where the HARQ indicator channel (PHICH) indicative of the negative response is transmitted but the control channel (UL-grant) for allowing the uplink shared channel (PUSCH, UL-SCH) to be transmitted is not transmitted; 3) a case where both the HARQ indicator channel (PHICH) indicative of the positive response and the control channel (UL-grant) for allowing the uplink shared channel to be transmitted are transmitted; and 4) a case where both the HARQ indicator channel (PHICH) indicative of the negative response and the control channel (UL-grant) for allowing the uplink shared channel to be transmitted are transmitted. i) a transmit power control unit configured to determine transmit power for a HARQ indicator channel (PHICH) indicating a positive response or a negative response to the uplink shared channel (PUSCH, UL-SCH); and ii) a transmitting unit configured to transmit a transmission signal to the user apparatus, the transmission signal including the HARQ indicator channel (PHICH) at the transmit power determined by the transmit power control unit, iii) wherein different transmit power for the HARQ indicator channel (PHICH) is set depending on (a) whether the transmission signal includes a control channel (UL-grant) for allowing the uplink shared channel (PUSCH, UL-SCH) to be transmitted or (b) whether the transmission signal includes the HARQ indicator channel (PHICH) indicative of the positive response; wherein i-1) the transmit power control unit is further configured to calculate the transmit power Power for the HARQ indicator channel (PHICH) in accordance with Power = Power Ref + CQI Ref − CQI + Δ, where Power Ref represents reference transmit power, CQI Ref represents reference radio quality information, CQI represents the downlink radio quality information, and Δ represents an offset, wherein the offset Δ is set to different values for the following four cases: 1) a case where the HARQ indicator channel (PHICH) indicative of the positive response is transmitted but the control channel (UL-grant) for allowing the uplink shared channel (PUSCH, UL-SCH) to be transmitted is not transmitted; 2) a case where the HARQ indicator channel (PHICH) indicative of the negative response is transmitted but the control channel (UL-grant) for allowing the uplink shared channel (PUSCH, UL-SCH) to be transmitted is not transmitted; 3) a case where both the HARQ indicator channel (PHICH) indicative of the positive response and the control channel (UL-grant) for allowing the uplink shared channel to be transmitted are transmitted; and 4) a case where both the HARQ indicator channel (PHICH) indicative of the negative response and the control channel (UL-grant) for allowing the uplink shared channel to be transmitted are transmitted. 1) a case where the HARQ indicator channel (PHICH) indicative of the positive response is transmitted but the control channel (UL-grant) for allowing the uplink shared channel (PUSCH, UL-SCH) to be transmitted is not transmitted; 2) a case where the HARQ indicator channel (PHICH) indicative of the negative response is transmitted but the control channel (UL-grant) for allowing the uplink shared channel (PUSCH, UL-SCH) to be transmitted is not transmitted; 3) a case where both the HARQ indicator channel (PHICH) indicative of the positive response and the control channel (UL-grant) for allowing the uplink shared channel to be transmitted are transmitted; and 4) a case where both the HARQ indicator channel (PHICH) indicative of the negative response and the control channel (UL-grant) for allowing the uplink shared channel to be transmitted are transmitted.