An electron pulse stretcher ring (STB ring)  at Laboratory of Nuclear Science (LNS) in Tohoku University provides quasi-cw electron beam for the study of nuclear physics. The extracted beam from the ring has certain spread in time and space resulted from the emittance of injected beam from linac even if the injected beam is perfectly matched to the ring optics. However, the extracted beam emittance can be reduced by applying a phase space manipulation. Under the effect of perturbation using an RF shaker driven by a mono-frequency, the betatron amplitude of circulating beam can be controlled in order to reduce the extracted beam emittance. We have demonstrated the reduction of emittance experimentally on the STB ring.