Beam test of a slow extraction by utilizing the 3rd order resonance has been performed to investigate the characteristics of the extraction system at TARNII and to develop a new technique with the slow extraction. High extraction efficiency was obtained by the extraction without accelerating beam. Time dependence of the profile of the extracted beam and micro-structure of the beam spill were measured. Furthermore we succeeded to extract the beam by a new method utilizing the emittance growth of the circulating beam in the ring. (author).