1. A background generation apparatus for generating a background by removing a moving object from an input image acquired by means of an image processing unit, the apparatus comprising: a feature vector extractor for extracting predetermined features at arbitrary positions in the input image to calculate input feature vectors; an average processor for calculating an average of the input feature vectors, and calculating base feature vectors in which outliers contained in the input image are suppressed; a data accumulator for accumulating the base feature vectors; a statistical processor for estimating the central value from time-sequential data representing the base feature vectors at arbitrary positions accumulated in the data accumulator, and calculating background feature vectors that are used to generate the background; and an average process result holder for holding the base feature vectors calculated, wherein the average processor includes: a feature vector subtractor for calculating a difference between an input feature vector and past base feature vector held in the average process result holder; and an average adder for adding to the past base feature vector, the difference multiplied by a predetermined coefficient.