The authors have been developing a seismic retrofitting method using concrete-filled steel tubular (CFT) members as a diagonal brace. The features of the method are easy set-up and low-cost because we made the enforcing devices lightweight and a simple connecting method to the existing structures. This method provides many advantages for the buildings located at the places where are difficult to transport heavy materials and equipment. An experimental construction for the seismic retrofit was conducted at the 2-story RC building on an isolated island in Japan. The construction was succeeded by only three persons in two days without heavy equipment. This paper is consisted of the reports of the constructing process and the loading test of the connecting part of the method. The trial construction includes a new detail of the connection. Two specimens were made and tested to estimate the lateral load carrying capacity of the connection.