This paper discusses a structural optimization for the reinforcement of the engine room of a ship with respect to the antivibration characteristics. To improve vibration characteristics of the structures, topology optimization methods can be effective because it can optimize fundamental characteristics of the structure due to its capability being able to change the topology of the target structure. In this research, we optimize the reinforcement of the engine room using the topology optimization for improving anti-vibration characteristics. First, an experimentally-observed vibration phenomenon is simulated using finite element method for frequency response problems. Next, the objective function used in the topology optimization is set as the dynamic work done by the load based on the energy equilibrium of the structural vibration. Then, the optimization problem is constructed by adding the volume constraint. Finally, based on the finite element analysis and the optimization problem, the topology optimization is performed for several vibration cases.