1. A method for measuring concentrations of blood components and analytes including at least one of glucose, cholesterol, albumin, hemoglobin, alcohol or drugs, the method comprising the steps of: (a) irradiating near infrared light onto skin of a subject containing blood-containing tissues and blood vessels; (b) receiving the near infrared light containing information on the blood component concentration, back scattered from or transmitted through the blood-containing tissues and blood vessels; (c) selectively outputting the light of at least three wavelengths from the received near infrared light; (d) converting the light of the at least three outputted wavelengths electrical signals, respectively; and (e) computing the blood component concentration using the electrical signals, wherein in step (c), assuming that A.sub.ic, i=1, 2,.. . , n, are absorption values of light of n wavelengths for the blood component being measured, the requirements for selection of the wavelengths are: (1) A.sub.1c is the maximum among A.sub.1c, A.sub.2c, A.sub.3c,.. . , A.sub.nc, and A.sub.2c, A.sub.3c,. .. , A.sub.nc are negligible when compared to A.sub.1c ; and (2) for other components, with the exception of the blood component being measured, the relation ##EQU14## is satisfied, where A.sub.ij is absorption value of wavelength i for blood component j, and n is the number of selected wavelengths.