Clarifying novel electronic properties of nanostructures provides key insights for future chemistry, nanoelectronics and quantum information technologies. Due to quantization of electron numbers, orbitals, and spins, quantum nanostructures show unique electronic and spintronic properties in the terahertz (THz) frequency range. We are working on physics of THz-matter interaction to explore new THz device principles at an ultrasmall nano region, i.e. single-molecule level. By characterizing and manipulating the properties of nanomaterials, we keep developing THz spectroscopy and molecular electronics.