A card-mounting rack for electronic part-mounting cards is disclosed by which a housing of a rack or the like produced in accordance with standard specifications can be used to mount a plurality of large cards in high density therein to achieve overall densification and miniaturization of a system such as a computer system. Cooling fans are provided on a front and rear faces of a housing of a rack. A mother board is horizontally placed at the center of the inside of the housing. A plurality of cards are mounted perpendicularly on top and bottom faces of the mother board using gondolas and driving mechanisms having a function for moving the cards upwardly or downwardly through a plurality of connector provided on the top and bottom faces of the motherboard. Further, spacers for stabilizing the cards are inserted on rear faces of the cards.