PURPOSE: To precisely inspect a translucent cylindrical body by casting light from one end side of the translucent cylindrical body while picking up an image with the use of an image pick-up means, and by extracting the contour of the cylindrical body from the image so as to trace the image along the contour.

CONSTITUTION: A rotary table 2 is rotated so as to a cylindrical cartridge 1 made of transparent glass is positioned at an inspecting station, and light projected from a light projector 4 and passing through the cartridge 1 is picked up by a TV camera 5 which delivers an image signal to an image processing device 7 in which the image picked up by the camera 5 is equally divided into a plurality of dots by horizontal scanning lines of the image signal and predetermined reference clock pulses. Then image signals corresponding to the dots are converted into brightness data so that they are binary-coded into darkness parts and brightness parts. Further, inverted binary coded signals corresponding to the dots are delivered as image data to a CPU 8. Further, the CPU 8 extracts the contour of the cartridge 1 from the inverted binary coded signals from the device 7, and traces the binary coded signals along the contour so that the presence of inferiority is detected.