A device and method for reducing noise of an external measurement sensor of mobility, including a storage unit that stores measurement values of an external measurement sensor of mobility including an ultrasonic sensor measuring distance values between the mobility and an object outside the mobility; and an operation unit that generates a plurality of functions capable of being derived from the measurement values stored in the storage unit, derives a final function having the most measurement values within a first range, among the plurality of functions, derives an estimated value that is an expected value of the measurement value through the final function, and selects a candidate final value that is the closest to the estimated value within a second range, among actual measurement values at a time point corresponding to the estimated value, as a final value.