Changes in speckle patterns due to certain external disturbances to be applied onto a multimode optical fiber were observed. In the first attempt, a multimode optical glass fiber was placed onto a support plate and a speckle pattern in an output light spot projected from the fiber was observed while rotating or tilting the support plate. The resultant speckle pattern appeared to be rotating in accordance with the rotation or tilt motion of the support plate, and the pattern rotation angle was almost proportional to the rotation angle of the support plate. In the second attempt, a jacket-covered communication-grade multimode optical glass fiber was placed in a load application section so that corrugated bending of the fiber was intentionally induced by means of alternately disposed plurality of ridges. When a certain level of load (up to 15 kg) was applied onto the fiber in the load application section and then removed, the number of speckles observed in an output light spot projected from the fiber showed decreases upon load application onto the fiber and then recovery with the load removal.