A circular dichroism measurement device includes: a sample part having a sample; a PEM that modulates a polarization state of an incoming light to the sample part or an outgoing light from the sample part; a photo detector that detects a change in a light intensity of the outgoing light from the sample part; an amplifier that amplifies a detection signal from the photo detector; an A/D converter that converts the detection signal amplified by the amplifier to a digital signal; and a digital processing device that executes a signal processing to the digital signal from the A/D converter to acquire a measurement value of circular dichroism of the sample. The A/D converter is configured to convert the detection signal, that is amplified in a state of containing the AC component and the DC component of the light intensity that changes with the same frequency as the modulation frequency of PEM.