A serial axial fan unit includes first and second motors with their base portions, i.e., first and second base portions axially facing each other. A motor gap is arranged axially between the first and second base portions. An axial length of the motor gap is preferably in a range from approximately 0.3 mm to approximately 2.0 mm. This configuration reduces transmissions of vibration of each of the first and second motors to the other, thereby reducing vibration interference between the first and second motors.