A sensor device comprising: a transmission signal generation unit for generating a plurality of mutually orthogonal transmission signals; a transmitting antenna unit for emitting the transmission signals generated by the transmission signal generation unit from a plurality of transmitting antennas (2-1 to 2-3), to which each of a plurality of antenna directivity patterns is allocated in a predetermined pattern, to space; a directivity switching unit for switching directivities of the plurality of transmitting antennas (2-1 to 2-3); an array antenna constituted by one or more receiving antenna elements (3-1 to 3-N) for receiving reflected waves of the transmission signals that are reflected by an observation target after being emitted from the plurality of transmitting antennas (2-1 to 2-3); a plurality of correlation process units (5-1 to 5-N) for performing a cross-correlation process between the plurality of transmission signals and reception signals of the receiving antenna elements (3-1 to 3-N) and outputting a plurality of signals after the cross-correlation process; a weighting unit for weighting the plurality of signals after the cross-correlation process outputted from the plurality of correlation process units (5-1 to 5-N) in accordance with an arrangement of the transmitting antennas (2-1 to 2-3) and the receiving antenna elements (3-1 to 3-N) and each of the plurality of preset antenna directivity patterns; and a signal combination unit for combining the plurality of signals after the cross-correlation process that are weighted by the weighting unit characterised by a timing control unit for controlling switching timing of the directivities by the directivity switching unit in order to maintain the orthogonality of the reception signals wherein when the directivity switching unit switches the directivities of the plurality of transmitting antennas (2-1 to 2-3), the transmission signal generation unit receives a switching command for switching the directivities of the plurality of transmitting antennas (2-1 to 2-3) from the timing control unit and stops, for a predetermined time, output of the transmission signals to the plurality of transmitting antennas (2-1 to 2-3). a transmission signal generation unit for generating a plurality of mutually orthogonal transmission signals; a transmitting antenna unit for emitting the transmission signals generated by the transmission signal generation unit from a plurality of transmitting antennas (2-1 to 2-3), to which each of a plurality of antenna directivity patterns is allocated in a predetermined pattern, to space; a directivity switching unit for switching directivities of the plurality of transmitting antennas (2-1 to 2-3); an array antenna constituted by one or more receiving antenna elements (3-1 to 3-N) for receiving reflected waves of the transmission signals that are reflected by an observation target after being emitted from the plurality of transmitting antennas (2-1 to 2-3); a plurality of correlation process units (5-1 to 5-N) for performing a cross-correlation process between the plurality of transmission signals and reception signals of the receiving antenna elements (3-1 to 3-N) and outputting a plurality of signals after the cross-correlation process; a weighting unit for weighting the plurality of signals after the cross-correlation process outputted from the plurality of correlation process units (5-1 to 5-N) in accordance with an arrangement of the transmitting antennas (2-1 to 2-3) and the receiving antenna elements (3-1 to 3-N) and each of the plurality of preset antenna directivity patterns; and a signal combination unit for combining the plurality of signals after the cross-correlation process that are weighted by the weighting unit characterised by a timing control unit for controlling switching timing of the directivities by the directivity switching unit in order to maintain the orthogonality of the reception signals wherein when the directivity switching unit switches the directivities of the plurality of transmitting antennas (2-1 to 2-3), the transmission signal generation unit receives a switching command for switching the directivities of the plurality of transmitting antennas (2-1 to 2-3) from the timing control unit and stops, for a predetermined time, output of the transmission signals to the plurality of transmitting antennas (2-1 to 2-3).