PROBLEM TO BE SOLVED: To reduce the device configuration of a lock-in amplifier and to easily cope with the change of frequency. SOLUTION: A light source part 11 generates the examination light including plural lights modulated by various frequencies. A light receiving part 12 receives the examination light generated from the light source part 11 and passed through a sample 20, and outputs an electric signal corresponding to the intensity of the received examination light. The lock-in amplifier 10 comprises an A/D converter 3 for outputting the digitalized data of an input signal, a reference signal memory 5 for storing the digitalized data of plural reference signals, a digital multiplier 4 for multiplying and outputting the digitalized data of the input signal outputted from the A/D converter 3 and the digitalized data of the reference signals read out from the reference signal memory 5, and a digital low-pass filter 6 for taking out the DC data from the output of the digital multiplier 4.
ORGANISM OPTICAL MEASURING DEVICE