In order to maintain low range sidelobe characteristics in signals of a reflected wave from a target even when the target moves, and to reduce interference among a plurality of sector radars, a first sector radar generates signals which are obtained by modulating a first code sequence at a first transmission cycle, obtained by modulating a second code sequence at a second transmission cycle, obtained by modulating the first code sequence at a third transmission cycle, and obtained by modulating the second code sequence at a fourth transmission cycle respectively. A second sector radar generates signals which are obtained by modulating the second code sequence at the first transmission cycle, obtained by modulating, at the second transmission cycle, a third code sequence having the opposite polarity to the first code sequence, obtained by modulating, at the third transmission cycle, a fourth code sequence having the opposite polarity to the second code sequence, and obtained by modulating the first code sequence at the fourth transmission cycle respectively. The first and second sector radars respectively transmit the generated signals from first and second transmission antennae.