The Solar Occultation FTS for Inclined-orbit Satellite (SOFIS) is a solar occultation Fourier transform spectrometer developed by the Environmental Agency of Japan, and onboard the Global Change Observation Mission-AI (GCOM- A1) satellite. GCOM-AI will be placed in a 650 km non-sun- synchronous orbit in 2006, with an inclination angle of 69 deg. SOFIS is the successor of the Improved Limb Atmospheric Spectrometer-II, which is onboard the Advanced Earth Observing Satellite-II (ADEOS-II). SOFIS measures the vertical profile of the atmospheric constituents with 0.2 cm-1 spectral resolution at 3 - 13 micrometers and 1 km vertical-resolutions. The target of SOFIS measurements is a global distribution of O3, HNO3, NO2, N2O, CH4, H2O, CO2, CFC-11, CFC-12, ClONO2, aerosol extinction, atmospheric pressure and temperature. SOFIS uses a double-pass flexible blade Fourier transform spectrometer (FTS) and a diode laser sampling system to reduce the size and weight of the apparatus. Two photovoltaic HgCdTe detectors and a pulse-tube cooler will provide high linearity and low-noise performance. SOFIS also has a visible (O2 A-band) grating spectrometer for pressure and temperature retrieval and a sun-edge sensor for detecting the tangent height position. This paper describes the conceptual design of the instrument and examines the test results of laboratory models of the FTS and the detector.