Interferometry has recently shown great advances in practical applications owing to progress and utility of electrooptic devices and computers. For objects of interferometry it is now strongly desired to measure such dynamic quantities as displacement, vibration, strain, and temperature. In this case rapid movement of interference fringes or speckle patterns has to be detected. However, the conventional image processing techniques using digital computers are not quick enough for this purpose. For reducing computation time it is necessary to endow the detector with a preprocessing function. One of the solutions is a spatial filtering detector with electronic scanning facility which has been used for three dimensional displacement meter  and for accerelating a laser speckle strain gauge . This detector, which consists of a photodiode array and its control circuit, delivers a voltage that is proportional to speckle displacement normal to the array. This paper reports applications of this detector to catch the movement of speckles and interference fringes obtained from optical fiber interferometers.