A barrier height measuring apparatus includes a conductive cantilever with a probe which is placed close to a specimen. The cantilever is elastically deformed by the interatomic force existing between the cantilever and specimen while the cantilever is oscillated. The displacement of the cantilever against the specimen is detected while the distance between the probe and the specimen is controlled to maintain the oscillation amplitude of the cantilever to a constant level. The apparatus includes a bias source for applying a voltage of a predetermined waveform between the specimen and the cantilever to cause a tunneling current to flow between them, and an arithmetic processor for calculating the barrier height of the surface of the specimen from the tunnel current and the displacement of the cantilever.