A cooling fan includes: a fan housing; a rotation shaft rotatably supported in the fan housing; a stator fixed to the fan housing; a rotor, which is provided with a magnet that is disposed with a predetermined gap away from the outer circumferential surface of the stator, and which has an impeller connected thereto; and a printed circuit board (PCB) which is installed on a lower side of the stator, and is equipped with a circuit component for controlling the cooling fan and a Hall sensor for sensing the revolutions of the rotor. In order to increase the sensing power of the Hall sensor, the magnet is formed such that the length or the width of the magnet at the lower part thereof that is adjacent to the Hall sensor is larger than that of the other parts of the magnet.