The 4D Space Access Neutron Spectrometer (4SEASONS) is a high-intensity Fermi-chopper spectrometer. It is intended to provide high counting rate for thermal neutrons with medium resolution (ΔE/E_i~6% at E=0) to efficiently collect weak inelastic signals from novel spin and lattice dynamics especially in high-T_c superconductors and related materials. To achieve this goal, the spectrometer equips advanced instrumental design such as an elliptic-shaped converging neutron guide coated with high-Q_c (m=3–4) supermirror, and long-length (2.5m) ³He position sensitive detectors (PSDs) arranged cylindrically inside the vacuum scattering chamber. Furthermore, the spectrometer is ready for multi-incident-energy measurements by the repetition rate multiplication method, which greatly improves the measurement efficiency.