A cartridge loading mechanism including a carrier movable between a first position where a magnetic tape cartridge having an openable shutter and a notch is inserted into the carrier and a second position where the cartridge is mounted onto a reel motor, and a shutter opening mechanism fixed to a base of a magnetic tape drive and having an engaging portion adapted to engage the shutter of the cartridge to open the shutter. The loading mechanism further includes a leaf spring mounted on the carrier and having a hook adapted to engage the notch of the cartridge, and a driving mechanism for moving the carrier between the first position and the second position. After the hook of the leaf spring comes into engagement with the notch of the cartridge at a third position during the movement of the carrier from the first position to the second position, the engaging portion of the shutter opening mechanism starts to engage the shutter of the cartridge.