HDD case (100) accommodates HDD device (60) having a disk medium and forms HDD unit (50). HDD unit (50) is removably disposed in an accommodating section of an electronic device. HDD device (60) has a substantially rectangular shape. Besides, HDD case (100) has a pair of side sections (120) located parallel to slot-in/pull-out directions in which HDD unit (50) is slotted into the accommodating section and is pulled out from the accommodating section. Further, protruding section (121) is formed on side sections (120) such that a part of side sections (120) is protruded on the outer side of HDD case (100). In a state where HDD case (100) is accommodated in the accommodating section of the electronic device, protruding section (121) makes contact with the side surface of the accommodating section.