An apparatus for measuring fruit properties, in order to classify fruit according to internal qualities, measures the sweetness of a fruit sample using near-infrared spectroscopy. The apparatus includes a pair of waveguides (12), a pair of optic emitter/sensor assemblies (14), a light-interrupting unit (20), and a light detector (40). The light detector calculates the intensity of light, transmitted from a light source and received by the optical emitter/sensor assemblies, thus allowing spectral analysis and interpretation for the determination of sweetness and acidity of a variety of fruits. The light detector controls the light-interrupting unit to interrupt the optical path when the light intensity is reduced. The apparatus is suitable for use in an automated line, for effective and reliable measurement of internal fruit properties, to improve operational efficiency and precision in fruit selection.