An electronic device is provided. The electronic device includes a first plate, a second plate having a flat surface and being at least partially formed of a polymer material, a housing, which encloses a space between the first plate and the second plate, is at least partially formed of a metal material, and includes a side member that is integrally formed with the second plate, wherein the side member has a first portion adjacent to a peripheral portion of the second plate, and the first portion has a first surface substantially facing in the second direction, contacts the peripheral portion of the second plate, and has a second surface facing in a third direction different from the first direction and the second direction.