A natural air cooled rack for vertically disposed printed boards. The rack comprises a plurality of stacked cases for housing printed boards. Each of the cases has draft openings on the upper surface and the lower surface thereof. An interspace is formed between one or more upper cases and the one or more lower cases. At least one supply opening and at least one exhaust opening are formed in the front portion of said interspace. The supply opening communicates with said draft opening on the lower surface of said upper case while said exhaust opening communicates with said draft opening on the upper surface of said lower case. Said exhaust opening is located substantially above said supply opening.