Provided is a method for measuring blood glucose levels of a subject with a portable apparatus for noninvasively measuring blood glucose levels including at least one light receiving element for detecting light by using different light integration times, including: (a) switching on an LED for emitting light having wavelength absorbed in or scattered by glucose (b) measuring a first signal value according to light which is reflected off the surface skin layer of the subject and enters in response to a first light integration time in the situation where the light is radiated (c) adjusting a second light integration time for measuring light reflected off the inner skin layer of the subject based on the first signal value (d) measuring a second signal value according to the light which is reflected off the inner skin layer of the subject and enters in response to the adjusted second light integration time and (e) producing the blood glucose level of the subject by using a third signal value according to light which enters due to an ambient environment and the second signal value in the situation where the LED is switched off.
