An apparatus for acquiring information on a time waveform of a terahertz wave is comprised of a terahertz wave-generating unit, a waveform information-detecting unit, and a delay unit for changing the time after the terahertz wave is generated in the generating unit until it is detected as waveform information of the terahertz wave in the detecting unit, wherein the delay unit is configured so as to change a propagating distance of the terahertz wave generated by the generating unit, and associates waveform information of the terahertz wave, which is detected in the detecting unit, and the propagating distance every terahertz wave generated by the generating unit.