A base station antenna apparatus for a mobile communication system, comprising transmission antennas (14-1 - 14-4), receiving antennas (24-1 - 24-4), two or more transmission paths, and two or more receiving paths, the apparatus being configured to feed a high frequency power signal of a radio signal frequency to the transmission antennas connected respectively to the two or more transmission paths and to synthesize reception signals received by the receiving antennas respectively connected to the two or more receiving paths, in which both the transmission antennas and the receiving antennas are respectively arranged in a vertical direction at a predetermined distance, the apparatus further comprising: transmission system detection means configured to individually detect if a signal level drops below a respective reference level thereby determining that an abnormality has occurred, in each of the transmission paths; receiving system detection means configured to individually detect if a signal level drops below a respective reference level thereby determining that an abnormality has occurred in each of the receiving paths; and control means configured, when an abnormal transmission path is detected by the transmission system detection means, to disconnect the abnormal transmission path from the corresponding transmission antenna and to correct deformation of directivity of the transmission antenna in a vertical plane caused due to abnormality in the transmission path by changing and setting a phase and an amplitude of a transmission signal in a normal transmission path, and, when an abnormal receiving path is detected by the receiving system detection means, disconnecting the abnormal receiving path from the corresponding receiving antenna and to correct deformation of directivity of the receiving antenna in a vertical plane caused due to abnormality in the receiving path by changing and setting a phase and an amplitude of a reception signal in a normal receiving path, wherein the correction of directivity of the transmission antenna in a vertical plane and the correction of directivity of the receiving antenna in a vertical plane by the control means are such that a tilt angle with its reference in a horizontal direction greater than a tilt angle of the electric wave imparted in normal states with no abnormality by an adjustment angle α is set, and wherein a magnitude of the adjustment angle α is configured to prevent variation of a service area resulting from increment of the half value width of directivity in a vertical plane which is due to reduction of number of operating transmission antennas from abnormality in a transmission path and to reduction of number of operating receiving antennas from abnormality in a receiving path. transmission system detection means configured to individually detect if a signal level drops below a respective reference level thereby determining that an abnormality has occurred, in each of the transmission paths; receiving system detection means configured to individually detect if a signal level drops below a respective reference level thereby determining that an abnormality has occurred in each of the receiving paths; and control means configured, when an abnormal transmission path is detected by the transmission system detection means, to disconnect the abnormal transmission path from the corresponding transmission antenna and to correct deformation of directivity of the transmission antenna in a vertical plane caused due to abnormality in the transmission path by changing and setting a phase and an amplitude of a transmission signal in a normal transmission path, and, when an abnormal receiving path is detected by the receiving system detection means, disconnecting the abnormal receiving path from the corresponding receiving antenna and to correct deformation of directivity of the receiving antenna in a vertical plane caused due to abnormality in the receiving path by changing and setting a phase and an amplitude of a reception signal in a normal receiving path, wherein the correction of directivity of the transmission antenna in a vertical plane and the correction of directivity of the receiving antenna in a vertical plane by the control means are such that a tilt angle with its reference in a horizontal direction greater than a tilt angle of the electric wave imparted in normal states with no abnormality by an adjustment angle α is set, and wherein a magnitude of the adjustment angle α is configured to prevent variation of a service area resulting from increment of the half value width of directivity in a vertical plane which is due to reduction of number of operating transmission antennas from abnormality in a transmission path and to reduction of number of operating receiving antennas from abnormality in a receiving path.