1. A signal processor for filtering digital signal values in a prespecified dimension measured along a preset route, comprising: a weighting factor calculating section for calculating a weighting factor for each of the digital signal values as well as for re-calculating and updating the weighting factor; and a filtration executing section for executing filtration using the calculated weighting factor to obtain a filter output value for each digital signal value, wherein the weighting factor calculating section comprises: a first zone generating section for generating a plurality of first zones by dividing the digital signal values into a plurality of first zones along the preset route; and a median calculating section for calculating a median for each of the first zones for a difference based on a sum of squares for respective components of the digital signal value and the filter output value for the digital signal value, wherein the weighting factor calculating section calculates the weighting factor based on the median in each of the first zones for the digital signal values in the respective first zones and updates the weighting factor.