Blower fan and working machine provided with the same

A blower fan comprising:

• a circular impeller having a base and a predetermined number of curved blades radially arranged at equiangular intervals on the base;
• a fan casing having an air-intake port disposed to face a central portion of a substrate of the impeller and eccentrically housing the blower fan and defining a spiral scroll passageway between an inner wall thereof and an external circumference of the impeller, the spiral scroll passageway having an inlet portion comprising a narrow nose portion and an outlet portion which comprises a wide discharge port;
• a driving source for rotating the impeller;
• a narrow nose portion that is a noise source of said fan, wherein a force of air within the fan is most greatly compressed in the inside of the spiral scroll passageway;
• and
• a sound-reflecting member made of a thin membrane, the sound-reflecting member being formed as a blind patch portion that covers part of the air intake port in order to minimize the noise to be released to the external environments from the narrow nose portion as a source of noise, where the blind patch portion is disposed at a position whose center is spaced away in an emanating direction of noise from the narrow nose portion by a distance corresponding to a half (½) of wavelength of noise.