A target detection system, comprising: a first target detection apparatus (S 1) for transmitting a first transmission signal, receiving a signal reflected by a target, and extracting first distance information about the target from a received signal; a second target detection apparatus (S 2) for transmitting a second transmission signal, receiving a signal reflected by the target, and extracting second distance information about the target from a received signal; and a processing device; the first and second target detection apparatuses arranged to operate for a plurality of targets in a monostatic mode and in a bistatic mode in which the first target detection apparatus is a transmitter and the second target detection apparatus is a receiver; characterised by the processing device calculating positions of said targets by: enabling the first and second target detection apparatuses to operate in the monostatic mode, acquiring the first distance information (r 11 and r 12) from the first target detection apparatus to each target respectively, and the second distance information (r 21 and r 22) from the second target detection apparatus to each target respectively, enabling the first and second target detection apparatuses to operate in the bistatic mode, acquiring, for each target, total propagation distance information (r 112 = r 11 + r 21; r 122 = r 12 + r 22) from the transmitter to the receiver through each target, making a provisional combination (r 11 and r 21; r 12 and r 22) of the first and second distance information and checking whether for each target a sum (r 11 + r 21; r 12 + r 22) of the first distance information and the second distance information in this combination minus the total propagation distance information (r 112 and r 122) for the said target satisfies an inequality by being below a threshold value (|r 11 + r 21) - r 112 | < ε; (r 12 + r 22) - r 122 | < ε), if the inequalities are satisfied, identifying positions of the plurality of targets by using the first distance information and the second distance information in the provisional combination, if one of the inequalities is not satisfied, identifying positions of the plurality of targets by using the first distance information and the second distance information in a combination (r 11 and r 22; r 12 and r 21) different from the provisional combination, checking whether the positions of the plurality of targets are positions in an monitor area, and determining that the positions of the plurality of targets are valid when the positions of the plurality of targets are the positions in the monitor area. a first target detection apparatus (S 1) for transmitting a first transmission signal, receiving a signal reflected by a target, and extracting first distance information about the target from a received signal; a second target detection apparatus (S 2) for transmitting a second transmission signal, receiving a signal reflected by the target, and extracting second distance information about the target from a received signal; and a processing device; the first and second target detection apparatuses arranged to operate for a plurality of targets in a monostatic mode and in a bistatic mode in which the first target detection apparatus is a transmitter and the second target detection apparatus is a receiver; characterised by the processing device calculating positions of said targets by: enabling the first and second target detection apparatuses to operate in the monostatic mode, acquiring the first distance information (r 11 and r 12) from the first target detection apparatus to each target respectively, and the second distance information (r 21 and r 22) from the second target detection apparatus to each target respectively, enabling the first and second target detection apparatuses to operate in the bistatic mode, acquiring, for each target, total propagation distance information (r 112 = r 11 + r 21; r 122 = r 12 + r 22) from the transmitter to the receiver through each target, making a provisional combination (r 11 and r 21; r 12 and r 22) of the first and second distance information and checking whether for each target a sum (r 11 + r 21; r 12 + r 22) of the first distance information and the second distance information in this combination minus the total propagation distance information (r 112 and r 122) for the said target satisfies an inequality by being below a threshold value (|r 11 + r 21) - r 112 | < ε; (r 12 + r 22) - r 122 | < ε), if the inequalities are satisfied, identifying positions of the plurality of targets by using the first distance information and the second distance information in the provisional combination, if one of the inequalities is not satisfied, identifying positions of the plurality of targets by using the first distance information and the second distance information in a combination (r 11 and r 22; r 12 and r 21) different from the provisional combination, checking whether the positions of the plurality of targets are positions in an monitor area, and determining that the positions of the plurality of targets are valid when the positions of the plurality of targets are the positions in the monitor area.