A sealed housing is provided with a body, a cover, and a movable fin for radiating heat while suppressing a change in internal pressure, and preventing invasion of water vapor or poisonous gas from the exterior to thereby avoid an accident caused by dew condensation, and corrosion of an electrical circuit component. The movable fin automatically slides toward the inside or outside of the sealed housing depending on a change in internal atmospheric pressure of the sealed housing following a change in internal temperature thereof. When the temperature inside the sealed housing rises due to heat from the electrical circuit component mounted in a package inside the sealed housing, a heat radiation area of the movable fin increases while keeping sealing tightness so that a heat radiation effect can be enhanced.