This study describes a development of thermal design scheme of a heat spreader for high-density packaging electronic equipment based on a topology optimization method. Thermal design of electrical equipment becomes more important to improve the reliability of products and more effective thermal design method is required to obtain more attractive design of the products. However, to output product designs coinciding user's variety needs, design limitations of cooling systems for dissipating heat from electrical devices are slightly increased. Therefore, a new thermal design scheme for the cooling devices should be developed in order to obtain enough heat dissipation performance under the limited design conditions. In this paper, we have proposed an application of topology optimization to a design method of a heat spreader panel mounted in a test model of a mobile electronic equipment that has some geometric features commonly found in thin electronic devices and equipment. Especially, we have investigated an optimum design of a heat conduction panel that is mounted on a PCB board and enhances thermal conduction between 5 heating chips and a heat sink. For an objective function, a miniaturization of maximum temperature and a range of the temperature variation in the panel were chosen and the investigation of the shape of the heat conduction panel was calculated by using topology optimization. Through the investigation, we evaluated an effectiveness of the topology optimization from the viewpoint of increasing the efficiency of thermal design process.