Recently, earthquakes occur over 30 times a year in Korea. In addition, earthquakes originating from the neighborhood countries were sensed in Korea and caused serious human casualties and economic loss. In Japan, U.S.A., New Zealand and etc., forces seismic design of building structures to prevent seismic damage. In Korea, seismic design has been applied to building structures with a scale larger than defined in the building code since 1988. However, serious seismic damages are expected for wall-type apartment buildings, which were designed before 1988 without application of seismic design. Therefore, appropriate seismic retrofitting methods that are economical and easy to construct are required for such buildings. In this study, seismic retrofitting methods using steel plates or sections are developed for the wall-type apartment buildings. Proposed retrofitting methods improve lateral stiffness of the wall-slab system without excessive increment of loads on base structure. The effect of retrofitting using plates, T-sections and H-sections was examined experimentally for wall-slap system test models. In the experiment, the performance of the joint and slab of the test models was improved and the retrofitting effect was proved to be excellent.