A protection device of a slot-in optical disk drive is provided. The protection device is disposed between two linking parts of the slot-in optical disk drive. One of the two linking parts is formed with a slot, and the other one of the two linking parts is connected to an upper end of a guide pin. A lower end of the guide pin protrudes and is inserted into the slot, and a portion of the guide pin corresponding to a side of the slot is formed with a notch. As the notch engages with the slot, the situation that the guide pin slides out of the slot can be avoided.