A fan includes an airflow guiding structure, an impeller and a guiding ring. The outer radius of the airflow guiding structure increases gradually from the top to the bottom of the airflow guiding structure. The airflow guiding structure includes a plurality of fins and a first space for accommodating a circuit device. The impeller is disposed on the airflow guiding structure and the impeller has a hub and several axial-flow blades disposed around the hub. The guiding ring is connected with the axial-flow blades. An inlet is formed on the top of the guiding ring, and an outlet is formed between the bottom of the guiding ring and the outer surface of the sidewall of the airflow guiding structure. When the impeller rotates, the airflow enters the fan from the inlet and flows along the outer surface of the sidewall of the airflow guiding structure, then the airflow exits the fan through the outlet. The direction of the airflow passing through the outlet is different from the direction of the airflow passing through the inlet.