Target searching means for searching in a target existing within a propagation space, which searches the target by using a traveling wave from a sound source making incident on the target within the propagation space and a forward scattering wave scattering forward from the target, the means comprising: sound source means for transmitting a sound wave of a probe signal into the propagation space; a transducer array placed in an area to receive the forward scattering wave of a data signal which scatters forward from the target existing within the propagation space; subtraction processing means for subtracting a traveling wave of a probe signal directly traveling from the sound source means towards the transducer array when the target is not within the propagation space, from a mixed wave of the forward scattering wave of the data signal and the traveling wave of the probe signal directly traveling from the sound source means towards the transducer array so as to separate the forward scattering wave of the data signal; passive-phase conjugate processing means for performing passive-phase conjugate processing on the forward scattering wave separated by the subtraction processing means so as to generate a passive-phase conjugated signal of the forward scattering wave; autocorrelation processing means for performing autocorrelation processing on the traveling wave which is the sound wave transmitted from the sound source means and which makes incident on an arbitrary position within the propagation space by having the sound source as a reference position so as to generate an autocorrelation processed signal of the traveling wave; and correlation means for judging a similarity between the autocorrelation processed signal and the passive-phase conjugated signal. sound source means for transmitting a sound wave of a probe signal into the propagation space; a transducer array placed in an area to receive the forward scattering wave of a data signal which scatters forward from the target existing within the propagation space; subtraction processing means for subtracting a traveling wave of a probe signal directly traveling from the sound source means towards the transducer array when the target is not within the propagation space, from a mixed wave of the forward scattering wave of the data signal and the traveling wave of the probe signal directly traveling from the sound source means towards the transducer array so as to separate the forward scattering wave of the data signal; passive-phase conjugate processing means for performing passive-phase conjugate processing on the forward scattering wave separated by the subtraction processing means so as to generate a passive-phase conjugated signal of the forward scattering wave; autocorrelation processing means for performing autocorrelation processing on the traveling wave which is the sound wave transmitted from the sound source means and which makes incident on an arbitrary position within the propagation space by having the sound source as a reference position so as to generate an autocorrelation processed signal of the traveling wave; and correlation means for judging a similarity between the autocorrelation processed signal and the passive-phase conjugated signal.