A sample analysis method is provided for analyzing a sample having a permeability to terahertz radiation and accurately measure the composition, physical properties, mass and dimensions of a very small sample or a minute amount of sample by irradiating the sample with terahertz radiation. In the method, a reflective member is provided adjoining a first principal surface of the sample, an entrance member is provided adjoining a second principal surface of the sample, terahertz radiation is delivered from outside of entrance member towards the sample, and the sample is analyzed using an interference wave generated from a first-surface reflected wave at the interface between the first principal surface of the sample and the reflective member and a second-surface reflected wave at the interface between the second principal surface of the sample and the entrance member.