When coherent light beams, i.e., laser beams are transmitted in an optical fiber and exit from one end to form an output light spot on a screen, non-uniform intensity distribution called speckle patterns is often recognized in the output light spot. The authors have confirmed that when a multimode optical fiber is placed in a loop or a U-shape onto a support plate and the support plate is rotated or tilted with the diameter of the loop or the longitudinal axis of the U-shape as the axis of the rotation or tilting motion, the speckle patterns appear to rotate in a certain direction. Such rotation phenomena of speckle pattern are observed with relatively good reproducibility, and the rotation angle of the speckle pattern is almost in proportion to the rotation or tilting angle of the support plate. In the authors’ previous reports, a rotation angle of speckle pattern was detected by manual work, which was tiresome and time-consuming task. This was also unrealistic if we are going to utilize the phenomena for some kinds of sensing application. In this paper, a new scheme for semi-automatically detecting the rotation angle of speckle pattern from image data before and after the pattern rotation is being tried. With this scheme, detection of the pattern rotation angle upon rotation or tilting of the support plate can be realized easily in a short period of time. The semi-automatic detection scheme has been actually employed to investigate rotation characteristics of speckle pattern in several different conditions.