A tape cartridge is arranged so that when an upper lid of a pocket portion of the tape cartridge is in a position for opening the upper side of the pocket portion, the upper lid is positioned above an upper surface of a casing body so that a lower surface of the upper lid faces the upper surface of the casing body through a gap in which a member of a recording/reproduction apparatus for depressing the cartridge can be placed. When the upper lid is in the position for opening the upper side of the pocket, the cartridge depressing member of the recording/reproduction apparatus is placed in the gap to depress the cartridge, whereby the cartridge can be stably depressed to and mounted in a predetermined position in the recording/reproduction apparatus when the cartridge is loaded in the apparatus.