This disclosure provides a fan, including a first case, a second case, and a reset mechanism. The first case includes a first side wall, where the first side wall has a first guide portion. The second case includes a second side wall, where the second side wall has a second guide portion. The first guide portion and the second guide portion are slidably joined and are configured to enable the first case and the second case to move toward or away from each other. The reset mechanism is connected to the first case and is configured to push the second case to move away from the first case.