A signal processing device that processes a bio-signal includes a lock-in amplifier chip configured to output a frequency-modulated modulation signal and enable one or more light sources to be driven in response to the modulation signal, and a multiplexer configured to receive and multiplex light sensing signals output from the light sources and then measured by multiple light measurement units, and the lock-in amplifier chip sequentially demodulates the multiple light sensing signals transmitted through the multiplexer.
