This study proposes a structural system which aims at improving the seismic performance of new and existing wooden houses making use of oil dampers. Problems to install any special damping devices into wooden structures are known, for one thing to be the wood being brittle in bending and the other the strength of the joint between the device and wood being relatively low. Therefore, to get rid of these problems, we developed an oil damper which works only when subject to compression and is provided with relief valves to limit the maximum resistance. First part of the study deals with a series of harmonic loading tests to see if the damper exhibits the same properties as designed beforehand. Then, the dampers are mounted as knee braces at the corners of wood panels which is subject to dynamic loading tests in two ways. First one is a test to apply sinusoidal inertial force to an isolated panel. Second one is a shaking table test on full scale single-story wood frames. From these tests, we confirmed that the damper can absorb as much as nearly 60% of seismic input energy. It is also confirmed that the installment of the damper makes it possible for wooden frames that collapses at the first strike of strong ground motion to withstand the same ground motion several times with no significant damage accumulation to main structures. Lastly, these test results are compared to analytical results and it is concluded that the proposed structural system do work to improve seismic safety of wooden houses.