An electronic apparatus is equipped with housing, a motherboard, a stud, and a lid. The housing constitutes an outer shell of the main body having a shielding property against electromagnetic radiation and an opening located on the bottom wall. The opening is smaller than the total mounting area of a plurality of extension modules which are layered each other. The motherboard is installed in the housing. The stud is attached on the bottom surface side of the motherboard and is fastened by a set of screws together with the plurality of extension modules. The lid has a shielding property against electromagnetic radiation and covers the opening.