According to rapid deterioration of many domestic tunnels and bridges, engineers that manage them have become insufficient. For this reason, it is desired to develop an automatic hammering robot that can inspect them quickly and accurately. If a hammering sound by the robot is similar to a sound by engineers, we can use human experiences for the accurate inspection. Therefore, we developed an underactuated hammering robot that can simulate a hammering sound by engineers. However, in case hammering direction changes, this robot cannot hammer with the same energy by the effect of gravity. To resolve this problem, we combined a swing slider crank mechanism and an underactuated mechanism, and controlled the height of a rotating shaft of crank according to hammering direction. In this paper, we clarified the relationship between hammering direction and the height of a rotating shaft of crank to control the hammering energy constantly. This energy control means velocity control of the hammering system. The experimental results showed the hammering energy is almost same in spite of direction. To verify the effectiveness of this inspection system, we carried out hammering tests in a tunnel using underactuated and fully-actuated systems and compared their frequency spectrums of the sounds. The frequency spectrums showed that the hammering sound of the underactuated system is more similar to a sound by engineers than fully-actuated system.