The present invention relates to a terahertz wave modulator. The terahertz wave modulator includes: a semiconductor substrate; a terahertz modulation layer including an organic-material layer disposed on the semiconductor substrate; and a first incident wave radiation unit for vertically radiating a first incident wave having a terahertz wave region onto the terahertz modulation layer. The transmitted terahertz wave may be variously modified according to the degree of crystallization of an organic material deposited on the semiconductor substrate and according to the intensity of incident light so as to maximize modulation efficiency using the modified terahertz wave. Thus, a device for modulating wavelength width, amplitude, and phase through waveform deformation in a time region may be provided. Furthermore, by bonding together a plasmons or metamaterials having similar surfaces, a highly functional terahertz wave modulation device may be provided, wherein said device may be widely used for optical purposes.