Moving body speed derivation method and moving body speed derivation program

A moving body speed derivation method that causes at least one computer to execute a process, the process includes deriving a reference point in a second moving body region that is an image of a second moving body, from one image capturing the second moving body among a plurality of time-series images captured by an imaging device installed in a first moving body; deriving a position of the second moving body based on a distance between the imaging device and a feature point in the second moving body corresponding to the reference point in the second moving body region; and deriving speed of the second moving body based on a change amount of the position of the second moving body corresponding to the second moving body region included in the plurality of time-series images.