The final goal of this study is to develop a buoyancy control device for underwater robots utilizing phase change of material. A conventional underwater robot and a conventional submarine adjust buoyancy by discarding a set of iron balls or seawater in other place, which is harmful to the environment. Therefore, we proposed new buoyancy control method utilizing phase change of material. Our previous method for inducing volume change use rubber for changing the volume, but rubber is not so strong. Therefore, we developed a new buoyancy control device using metallic bellows. The control part of the device is within a robot body to prevent it from suffered from water. As a result of experiments, we confirmed that the durability of the device was improved without suffering heat and cooling ability.