PROBLEM TO BE SOLVED: To perform altitude measurement of an object to be measured by simple structure without using many antenna elements.SOLUTION: An altitude measuring apparatus comprises: an envelope detection part which detects an envelope signal of a signal generated by interference between a first signal and a second signal and outputs the envelope signal as an amplitude fluctuation signal when a signal radiated from an object to be measured with unknown altitude comes to a measurement subject as the first signal and the second signal via different routes; a fundamental frequency detection unit which calculates a fundamental frequency from the amplitude fluctuation signal; a parameter acquisition unit which acquires a horizontal position, the altitude, speed of the measurement subject, and a horizontal position of the object to be measured; and an altitude operation part which calculates the altitude of the object to be measured according to a predetermined operational expression by using a parameter ac
