The goals of my works are precise measurements of magnetic transition in even-valence transition metal and high speed manipulation of spin state using recently-developed terahertz technology based on ultrashort pulse technique. Terahertz (THz) frequency region (0.1-10THz) lies in intermediate region between light and electric wave. Because both electric current J and polarization dD/dt contribute to a dielectric response, simple approximation and technique for high/low frequency limit is not available. In spite of awkward electromagnetic wave, valuable dielectric responses decisive for physical properties lies in this frequency region, so techniques of generation, detection, and the interpretation of the electromagnetic radiation response have been rapidly developed. Similarly, both magnetic response M of the low frequency and magneto-optic response Pxy of the high frequency contribute to the magnetic response. However, the magnetic resonance of the even number spin system such as Fe2+ appears in the terahertz even without strong magnetic field. This transition is important for various medical applications, and high-frequency magnetic transition is expected to bring various potentials of large oscillator strength, existing in ground state at high temperature, and high speed driving of spin state. Up to now, the ESR measurement with strong magnetic field has been performed. If precise spectroscopy technique in THz frequency region and nonlinear spectroscopy, similar scheme of NMR measurements using high power THz wave are available, new conventional THz sensing and spin manipulation technique should be opened. One of my trials is access to magnetic transition in even-valence transition metal with narrow band using advanced terahertz oscilloscope, based on asynchronous optical sampling methods. High-power THz wave generation and the enhancement of magnetic field bring to sin echo measurements, which allow us to manipulate spins directly with magnetic- resonant THz pulses.