Abstract: A wave-leakage measuring apparatus compares the power density of the leakage waves, in the portions on the upper side, the lower side, the left side, the right side of the high-frequency heating apparatus which is being measured in two steps, with the leakage locations by a central data processing computer to select one of the maximum wave-leakage locations. The apparatus then brings one of the power-density detectors to the maximum wave-leakage location by a robot and precisely measures the power density of the leakage waves while a wave-mode converting apparatus of the high-frequency heating apparatus which is being measured makes at least one rotation. The apparatus then automatically determines the acceptability of the measured values by the central data processing computer.