PROBLEM TO BE SOLVED: To compensate for acoustic mode dependency of concentration measurement sensitivity to a constituent to be measured.SOLUTION: Two of laser diodes 1-1 to 1-3 perform intensity modulation of light of two waves having different wavelengths by signals having the same frequency and different phases and perform irradiation. A photoacoustic cell 13 becomes a resonator for amplifying a photoacoustic signal generated from an object 12 to be measured. An acoustic sensor 7 detects a photoacoustic signal. An information processor 11 estimates an acoustic mode, based on the amount of change in light intensity obtained from a measurement result of the light intensity when the strength of a measurement signal is minimized in each case of two cases in which the wavelength of light for changing intensity differs, and based on the amount of change in light intensity obtained from a data set, and determines a correction coefficient of concentration measurement sensitivity to a constituent to be measured, based on the acoustic mode, and a known relationship between the concentration measurement sensitivity to a constituent to be measured included in the object 12 to be measured and the acoustic mode.SELECTED DRAWING: Figure 3【課題】測定対象の成分に対する濃度測定感度の音響モード依存性を補償する。【解決手段】レーザダイオード１－１～１－３のうちの２つは、異なる波長の２波の光を同一周波数で且つ異なる位相の信号により強度変調して照射する。光音響セル１３は被測定物１２から発生する光音響信号を増幅する共振器となる。音響センサ７は光音響信号を検出する。情報処理装置１１は、強度を変化させる光の波長が異なる２つの場合について、それぞれの場合で測定信号の強度が最低となったときの光強度の測定結果から得られる光強度の変化量と、データセットから得られる光強度の変化量に基づいて音響モードを推定し、この音響モードと、被測定物１２に含まれる測定対象の成分に対する濃度測定感度と音響モードとの既知の関係に基づいて、測定対象の成分に対する濃度測定感度の補正係数を決定する。【選択図】 図３
