A biological signal detection device includes a reference pulse generation unit, a photo-reflector, a reference voltage control unit, a variation amount detection unit, and a biological signal generation unit. The reference pulse generation unit generates a reference pulse train having a variable frequency. The photo-reflector generates a photo-reflector output signal train in response to the reference pulse train. The reference voltage control unit provides a reference voltage. The variation amount detection unit receives the reference voltage and the photo-reflector signal train and generates a variation amount detection signal train. The variation amount detection signal train is provided to the biological signal generation unit to correct the frequency of the reference signal pulse train and to the reference voltage control unit to adjust the reference voltage signal. Adjusting the frequency of the reference pulse signal train improves sensitivity and adjusting the reference voltage signal maintains accuracy of the device.
