A disk cartridge ejection mechanism in which a disk cartridge is moved from a loading position where recording and reproducing of information are possible for a medium in the cartridge to a cartridge-removable position where the cartridge can be taken out of an information recording and reproducing apparatus, wherein there are provided a cartridge engagement device that engages with the cartridge when the cartridge moves from the loading position to the cartridge-removable position to prohibit the cartridge to move beyond the cartridge-removable position, a cartridge engagement assistance device that prevents releasing of engagement of the cartridge engagement device for the cartridge, when the cartridge moves to the cartridge-removable position and an assistance releasing device that releases the state wherein a cartridge engagement assistance device that prevents releasing of engagement of the cartridge engagement device, after the cartridge moves from the loading position to the cartridge-removable position.