A non-invasive optical internal substance detector includes: a diode array including a plurality of light emitting diodes (LEDs) for emitting light toward a target where an internal substance is detected, and a plurality of photodiodes (PDs) for receiving light which is reflected from the target after being emitted from the plurality of light emitting diodes； and a controller for controlling the plurality of light emitting diodes to be turned on or off and for processing a signal obtained from the photodiodes. The plurality of light emitting diodes and the plurality of photodiodes each have a size of several micrometers to several tens of micrometers and are arranged at intervals of several micrometers to several tens of micrometers from each other.
