The present invention makes it possible to obtain appropriate speed deviation data for switching between an accelerator and brake that corresponds to inclination in a standard mode. A vehicle speed deviation calculation method for calculating vehicle speed deviation for switching from an accelerator to a brake when a vehicle is made to travel according to a standard mode (driving target vehicle speed) of a vehicle driving pattern defined on the basis of time and vehicle speed within a range deviating from the standard mode by a prescribed speed and prescribed time, wherein the vehicle speed deviation for switching from an accelerator to a brake from a determination reference point A as of the current time to a reference point E for switching from the accelerator to the brake as of the current time is calculated through the calculation of a standard mode slope AB through the approximate differentiation of the vehicle speed at the determination reference point A as of the current time on the standard mode of th
