Generation of a light source and a light pulse train for generating light generated by the light source, in which a carrier wave is coherent, interference between adjacent waveforms is low, and a spatial length of a pulse width is smaller than a depth range of an observation target region of an object to be measured. Device, a frequency shifter for converting the frequency of the optical pulse train modulated by the generator, an optical path length changing unit for changing the optical path length of the optical pulse train, an optical pulse train output from the optical path length changing unit, and an object to be measured. A photodetector to which a backscattered wave from an object is input, a filter for extracting a difference signal having a shift frequency of the frequency shifter, which is output from the photodetector, and a difference signal extracted by the filter, A demodulator that synthesizes a reference signal synchronized with the shift frequency of the frequency shifter, and an analysis unit that analyzes the signal output by the demodulator.光源と、前記光源が発生した光を、搬送波がコヒーレントで、隣接する波形間の干渉が低く、測定対象物の観察目標領域の深さ範囲よりパルス幅の空間長が小さい光パルス列を生成する生成器と、前記生成器によって変調された光パルス列の周波数を変換する周波数シフタと、前記光パルス列の光路長を変更する光路長変更部と、光路長変更部から出力される光パルス列と、測定対象物からの後方散乱波とが入力される光検出部と、前記光検出器から出力される、前記周波数シフタのシフト周波数を有する差信号を抽出するフィルタと、前記フィルタが抽出した差信号と、前記周波数シフタのシフト周波数に同期した基準信号とを合成する復調器と、前記復調器が出力した信号を解析する解析部と、を備える。
