1. A scanning tunneling microscope comprising: a probe; a control unit that controls a distance between the probe and a sample; a voltage applying unit that applies a non-modulated direct current voltage between the probe and the sample; a measurement unit that measures a tunneling current that flows between the probe and the sample by the direct current voltage; an extraction unit that extracts as an observation value a specified frequency component from instantaneous values of the tunneling current measured by the measurement unit; and an observation information generation unit that generates observation information that includes information relating to at least one of a chemical state and an internal structure of a surface of the sample on the basis of the observation value extracted by the extraction unit.