PURPOSE: To simplify the mechanism, and to execute the processing at a high speed by measuring an optical fiber axial shift component in two directions, or an absolute position of an individual optical fiber, from a single image by a fixed TV camera.

CONSTITUTION: A lamp 3 is fixed to an objective lens 2 or a lens barrel 9, and fixed so as to have a specified angle α against an optical axis of the objec tive lens 2. Also, an observation system is set to a fusion slicing device 10, so that the optical axis of the objective lens becomes vertical to an arranging direction of an optical fiber which has been set on the weld connecting device 10. An image which has been caught by a TV camera under a specified condi tion is sent to an image processing unit 7 by a cable 8a, analyzed therein, and an axial shift quantity is calculated. In this image processing unit 7, a microprocessor and a memory are contained, and after the processing has been ended, its result is sent to the fusion slicing device 10 through a cable 8b, and based on it, the operation which is executed in the next time is selected by a controller provided in the weld connecting device 10, and the slicing operation is advanced automatically.