Copyright © 2014 CC-BY-3.0 and by the respective authors.Stable electron beam position and energy are crucial for stable operation of Free Electron Laser (FEL) both in single-pass and oscillator configurations. In order to increase stability of FEL output power and wavelength, three feedback control loops based on beam position measurements have been introduced to an S-band linac driving the mid-infrared oscillator type FEL at Kyoto University. The beam position and energy of the electron beam have been successfully stabilized. The achieved stability of FEL output power was 10%-FWHM at the wavelength of 12 μm. The wavelength stability of the FEL was estimated to be 0.3%-FWHM from measured electron beam energy fluctuation.