A variable wavelength generating method and an apparatus thereof, for use in measuring a body fluid constituent concentration. The apparatus includes: a thermo-electric cooler (TEC) whose temperature is varied depending on a change in a supplied current a light source section generating a wavelength that is varied depending on a temperature change of the thermo-electric cooler a current supply control section controlling a current supplied to the TEC an operation power source generation section supplying an operation power source for performing synchronization so that an operation of the light source section may be performed and a controller for adjusting a current flowing in the TEC adjusting the operation power source supplied to the light source section.
