A recording medium is provided wherein type determination and writing possibility determination is enabled for various types of disks. Opening and closing structure functions to open and close a detection hole of a cartridge. The structure forms a plane substantially horizontal level with a reference plane of the cartridge at a position of a detection hole when the detection hole is in a closed state. The cartridge has at least a first detection hole and a second detection hole formed therein. The second detection hole (H1) is opened and closed by the opening and closing structure, and the first detection hole (H0) is in an open state at all times.