Cartridge housing formed to protect disk-shaped medium from dust-particles

A disk-shaped information memorizing medium cartridge, comprising:

• a cartridge housing including a disk-shaped information memorizing medium accommodating room formed by superposing a pair of shells;
• a disk-shaped information memorizing medium arranged for rotating freely in said disk-shaped information memorizing medium accommodating room;
• an opening window formed in one shell of said pair of shells, said opening window exposing an information memorizing surface of said disk-shaped information memorizing medium;
• and
• an opening and closing door installed in said one shell of said pair of shells for swinging freely and for opening and for closing said opening window when swinging within a plane of said one shell of said pair of shells as a guide, wherein said plane of said one shell is substantially parallel to said information memorizing surface of said disk-shaped information memorizing medium rotatably arranged in said disk-shaped information memorizing medium accommodating room, wherein
• a lock mechanism is provided in said cartridge housing for locking said opening and closing door at a position where said opening window is closed, and
• said lock mechanism comprises a first lock mechanism to engagingly stop a lock pin provided at a first end of said opening and closing door and a second lock mechanism to engagingly stop a lock nail provided at a second end of said opening and closing door.