PROBLEM TO BE SOLVED: To provide an apparatus to highly accurately measure a constituent concentration such as a blood glucose concentration.SOLUTION: Laser diodes 1-1 and 1-2 modulate intensity of light of two waves with different wavelengths by the same frequency and by signals of different phases, and irradiate an object 13 to be measured with the light. An information processing device 12a changes the power of light emitted from the laser diode 1-2, and measures the power of the two lights, the intensity of an electric signal output from a lock-in amplifier 11, and one of two modulation voltages for controlling the power of the two lights, acquires the powers of the two lights corresponding to the modulation voltage from the value of the modulation voltage at the time when the intensity of the electric signal reaches a minimum level, calculates a difference between the powers, and derives a constituent concentration of an object to be measured contained in the object 13 to be measured from an amount of change in the light power with an amount of change in the difference of power at two different time points as the amount of change in the light power.SELECTED DRAWING: Figure 1【課題】血液グルコース濃度等の成分濃度を高い精度で測定する装置を提供する。【解決手段】レーザダイオード１－１，１－２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被測定物１３に照射する。情報処理装置１２ａは、レーザダイオード１－２から放射される光のパワーを変化させて、２つの光のパワーと、ロックインアンプ１１から出力される電気信号の強度と、２つの光のパワーを制御するための２つの変調電圧のうちの一方とを測定し、電気信号の強度が最低となったときの変調電圧の値から、この変調電圧に対応する２つの光のパワーを求めてこれらのパワーの差を計算し、異なる２つの時点におけるパワーの差の変化量を光パワー変化量として、光パワー変化量から被測定物１３に含まれる測定対象の成分の濃度を導出する。【選択図】図１
