Cartridge holder apparatus and magnetic recording/reproduction apparatus including same

A disclosed cartridge holder apparatus includes: a cartridge supporting member having a lateral plate portion and side plate portions on both sides thereof; a cartridge upper surface supporting member disposed between the side plate portions on both sides of the cartridge supporting member; a support mechanism of a cartridge upper surface supporting member for supporting the cartridge upper surface supporting member so as to form a cartridge housing space in accordance with an inserted cartridge; and a cartridge gripping mechanism supported by the cartridge upper surface supporting member and the support mechanism of a cartridge upper surface supporting member. The cartridge gripping mechanism changes positions in the vertical direction, while a locking portion for locking a lock-receiving portion of an inserted cartridge maintains a position in a cartridge insertion direction.