Optical systems of compound eyes are of great interest in the study of micro-optics. We propose an artificial visual sensor in a model of the apposition eye of an insect. As a key component unit of the visual sensor, a sensor array consisting of 16 x 16 individual optical sensors each with a small view field is fabricated and examined. To achieve both the practical assembly and the compact size of the sensor array, a photodiode array, a glass substrate with a pinhole array, and a group of rod-type gradient-index microlenses are stacked. The optical thickness of the sensor array is 2.9 mm. Because of the low intensity of light received by the photodiode the photocurrent is amplified 107 times in current-to-voltage conversion efficiency. The fabricated sensor array produces a mosaic image with 16 x 16 pixels and eight shades of gray scale. By arranging several of these sensor arrays along a circumference, a wide-field-angle visual sensor similar to a compound eye could be realized.