An apparatus for measuring a glucose concentration is noninvasive, accurate, and compact. The apparatus includes a detection unit (10) and a principal component analysis (PCA) unit (20). The detection unit includes a light source (11) to emit mid-infrared light, an ATR prism (12) to receive the mid-infrared light with a measuring object placed on the ATR prism, and a spectrum detector (13) to detect an absorption spectrum from the mid-infrared light from the ATR prism. The PCA unit includes a loading memory (24) to store a glucose corresponding loading and a personal data memory (28) to store personal data in the form of a calibration curve. According to the detected absorption spectrum, stored loading, and stored personal data, the PCA unit computes a glucose concentration of the measuring object.