Abstract: Infrared cameras (51, 54) and infrared illuminators (53, 55) thereof are opposed to each other across a transparent belt (41a). The infrared cameras (51, 54) photograph the front sides and the backsides of pitted fruits (prunes) which are conveyed by a conveyor (41) of the transparent belt (41a). A region of the fruit at a predetermined level or lower is determined based on the photographing data of the infrared cameras (51, 54), an average brightness level on the edge surface of the fruit region is determined, a depressed portion at a predetermined level or lower is determined based on the determined average brightness level, and it is decided whether a seed fragment remains in the fruit based on the shape of the depressed portion that is a characteristic of a measurable brightness level (shade) property.