In a unit holding mechanism, a first slide lever 31 and a second slide lever 32 are slidable in directions different from those of a third slide lever 41. Thus, it is possible to prevent an erroneous removal of battery units 21 and 22 and an HDD unit 23. More specifically, since the sliding directions of the slide switches vary with the type of unit to be loaded/unloaded, a user can identify the unit to be loaded/unloaded by examining only the sliding directions of the slide switches by the touch. Thus, even if the user attempts to remove the unit without viewing a bottom surface 1b of a first housing 1, it is possible to reduce the possibility of a misoperation in which a unit other than the intended unit is removed erroneously.