[en] Relations between relevant accelerator types and free electron laser (FEL) wavelengths are reviewed and a difference between FEL spectra at oscillation and amplification is discussed. FEL performance limitations related to the electron beam emittance and relative energy spread are also discussed for 0.3-μs FEL oscillations FELI is aiming at by the end of 1996. Recent developments of FEL accelerators and FEL facilities including FELI linac and IR ∼ UV-FEL facilities are reviewed. Features of FELI electron linac including a 5-MeV injector and IR ∼ UV-FEL facilities are introduced. The linac is operated in three modes of 24 μs, 12.5 μs and 0.5 μs. With a choice of three modes, the maximum accelerated energy can be changed from 165 MeV to 288 MeV. The linac beam is sent to four undulators using S-type BT systems installed at 30-MeV, 75-MeV, 120-MeV and 165-MeV at a 24-μs pulse beam load. The beam used for lasing at 30-MeV and 75-MeV section, can be reaccelerated and reused for lasing. The prospect and cost of FEL generators covering FIR, IR, UV and shorter wavelength are also discussed. (author)