The spectrometer includes a spectrometer body; a shield including a layer on an exterior of the spectrometer body to prevent light from entering and escaping through an area other than a contact surface between the spectrometer body and an object; an internal light source placed within the shield and configured to emit light to the object; a spectroscope mounted in the spectrometer body and configured to allow the light that passes therethrough to be casted into a spectrum; a detector configured to have one surface that is in full contact with the spectroscope and to detect external light entering from outside of the shield; and a processor configured to, in response to the detector detecting the external light, perform a certain processing.