An image analysis device installed on a vehicle for detecting objects that are likely to affect the vehicle. An image processing unit included in the image analysis device sets a seeking area in a left-hand image of the field, and calculates a moving increment for seeking "Step" using a variable "n". A correlation calculation process is sequentially executed in the seeking area set in the left-hand image of the field while moving a reference image stepwise at the moving increment "Step" so as to obtain a correlation area that gives the highest degree of correlation, and then a new seeking area is set, which consists of the correlation area and horizontally arranged two areas that sandwich the correlation area, and the moving increment "Step" is decreased in order to reduce the amount of calculation.