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 of the airflow guiding structure 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 has a hub and several blades. The guiding ring connects to the airflow guiding structure via at least one connecting element. A predetermined distance is arranged between the inner surface of the guiding ring and the outer edges of the blades. An inlet is formed at the top of the guiding ring, and an outlet is formed between the bottom of the guiding ring and the outer surface of a 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.