An apparatus that detects creeping of radar waves includes: a transmitter transmitting radar waves; a receiver receiving incoming waves from a target; a distance detecting unit detecting a first distance which is a distance up to the target; a speed derivation unit deriving a relative speed relative to the target; a distance estimating unit estimating, based on the relative speed, a second distance which is a distance up to the target; and a creeping detecting unit determining whether or not a creeping has occurred in accordance with whether or not the differential distance representing a deviation quantity between the first distance and the second distance is larger than or equal to a predetermined threshold.