To reduce noise due to blade noise of a multiblade blower used in internal cooling of a liquid crystal projection type display device such as a liquid crystal projector, and alternatively, to improve cooling performance by increasing an air flow amount when noise levels are the same.

The multiblade blower carrying out internal cooling of a projection type image display device includes a multiblade impeller 19, an air passage 30 annularly formed around the multiblade impeller from an inlet port to an exhaust port 13 of the multiblade blower, and a casing 14 provided with a plurality of resonance boxes 17 in an outer side of the multiblade impeller along the air passage. The number of the resonance boxes provided in an exhaust port neighborhood 33 of the air passage is provided more than the number of resonance boxes arranged in a midstream part 32 of the air passage, or the resonance boxes are arranged in a plurality of rows in an axial direction of the multiblade impeller.