Provided are an in-blood component measurement method, an in-blood component measurement device, and an in-blood component measurement program, enabling more accurate measurement of a proportion of glycohemoglobin in the total hemoglobin concentration in blood. The in-blood component measurement method is designed to have a constitution including the steps of irradiating, with near-infrared light, blood that is a target to be measured for a proportion of glycohemoglobin in the total hemoglobin concentration in blood, receiving transmitted light of the near-infrared light passing through the blood, measuring an absorption spectrum of the blood on the basis of the transmitted light received, and calculating the proportion for the blood that is the target of measurement by comparing absorbance at a first wavelength range including 1450 nm in the measured absorption spectrum to absorbance at the first wavelength range in the absorption spectrum of blood in which the proportion is already known.
