Disc cartridge having improved shutter

A disc cartridge comprising:

• a casing comprising an upper casing member and a lower casing member joined together to define an interior space in said casing, said casing having at least one pickup inserting hole therein;
• a disc mounted in said casing so as to be rotatable therein;
• and
• a shutter having a substantially U-shape and comprising upper and lower shutter plates and a slider for connecting said upper and lower shutter plates to each other, said slider being slidably fitted on said casing for covering and uncovering said pickup inserting hole;
• said slider including a first side wall arranged on the side of said slider to which the slider moves to uncover said pickup inserting hole, said first side wall having an opening;
• a shaft engagedly fitted in said opening, said slider being guided on said shaft, and also including biasing means urging said shutter in the direction of covering said pickup inserting hole;
• said casing having an inner surface defining said interior space, said inner surface including guiding means;
• said slider also including a second side wall on the opposite wall of said slider with respect to said pick-up inserting hole and having guided means comprising a projection which slidably engages with said guiding means of said casing.