1. A method for measuring a speed of a moving body using an accelerometer, comprising the steps of: setting a standard for regulating one or more windows, each of which window is a range of time for obtaining a movement average for a movement measurement value at a point of time from a plurality of movement measurement values measured by the accelerometer and a plurality of weight values for each of the measurement values included in the windows; storing the measurements measured by the accelerometer; determining whether the moving body has stopped at a point of time when the speed of the moving body is to be measured; detecting an irregular constant of the accelerometer and a gravitational acceleration component at a stopped condition when the moving body has been determined to be in a stopped condition; regulating the windows and the weight values based on a predetermined standard for regulating the windows and the weight values when the moving body has not been determined to be in a stopped condition; detecting the irregular constant of the accelerometer for measuring the gravitational acceleration component and the gravitational acceleration component at the point of time, based on information in the windows and the weight values regulated during the regulating step; and calculating an actual acceleration value at a pertinent point of time by subtracting the irregular constant and the gravitational acceleration component from the acceleration measurement at the point of time and calculating the speed of the moving body based on the actual acceleration value.