Abstract: There is provided a system in which when a gate having a reflection level of a threshold or higher and having been recognized as a control target by last time is not recognized as the control target this time, the gate is assumed to be actually detected, and extrapolation device extrapolates the gate (see ?) up to a predetermined number of times (five times), wherein when the gate is a stationary object, and a reflection level of the gate at the next detection (Time 6) predicted from a reflection level at the previous detection (Time 4) and a reflection level at the current detection (Time 5) is lower than a detection threshold (see ?), the limit of the number of extrapolations by the extrapolation device is reduced from five to two.