1. A region extracting method, said method comprising the steps of: executing a concatenated region expansion process on objective multi-dimensional data to extract a desired region from said objective multi-dimensional data, said concatenated region expansion process starting from one or more data points extracted in said desired region and including repetition of an expansion substep in which time series data indicating a transition of the number of data points having connectivity with each other is set and a plurality of data points are incorporated into said extracted data points when said plurality of data points are adjacent to previously incorporated data points and satisfy expansion criteria; displaying the incorporated extracted data points on a display screen; inversely tracing said concatenated region expansion process, when the incorporated extracted data points overflow the desired region into an external region, by using said time series data indicating the transition of the number of data points having connectivity with each other; identifying a connection part between the desired region and an overflow region of said incorporated data points on the basis of said time series data, said overflow region being located outside of the desired region; and deleting the overflow region according to the connection part from the incorporated extracted data points.