We are conducting experiments to generate self-amplified spontaneous emission (SASE) in the far-infrared region and to measure its characteristics, using a single bunch electron beam accelerated with the L-band linac at ISIR, Osaka University. We have measured the wavelength spectra of SASE in the wavelength region between 80 and 180μm using a grating monochromator and a Ge:Ga detector. The measured spectral widths of the fundamental peak are slightly larger than those predicted by the one-dimensional model. We have also observed the second harmonic peak of SASE.