There are provided a terahertz wave spectral dispersing unit 13 for spectrally dispersing a terahertz wave to be generated from a terahertz wave generating semiconductor 12 into two waves, a terahertz wave focusing unit 14 for focusing a terahertz wave transmitted through a sample liquid film 101 and a terahertz wave transmitted through a reference liquid film 102, and a terahertz wave detecting semiconductor 15 for detecting the focused terahertz wave, and it is possible to detect the terahertz wave transmitted through the sample liquid film 101 and the terahertz wave transmitted through the reference liquid film 102 in an interference state, thereby offsetting a noise made by a stripe-shaped wave generated on the sample liquid film 101 and a noise made by a stripe-shaped wave generated on the reference liquid film 102.