Abstract: A device for checking sheet packaging, whereby all the defects of packaged articles or sheets are easily and highly accurately detected based on the density or color distribution of reflection and transmission images. Defects such as deformation, discoloration, foreign matters and contamination of an article (16) packaged with a sheet and the sheet are detected by forming a density distribution code image or color code distribution image or by executing inter-image calculation based on a reflection image, a transmission image, or density or color images thereof. The upper and lower light sources are simultaneously turned on to separately form a reflection image and a transmission image from the input image in order to enhance the checking efficiency. Furthermore, a reflector (17) is disposed under a packaging sheet to enhance image contrast and to improve checking efficiency and stability. Optimum conditions for the kind and position of the reflector are clarified.