To facilitate the assembling of a partitioning member and to reduce the manufacturing cost by pressing a sound absorbing member toward a casing by the partitioning member to hold it, and pressing the partitioning member toward the casing by the elastic force of the sound absorbing member to hold it.

A sound absorbing member 147 consisting of a porous elastic member is provided in a position corresponding to a sound absorbing range between a first casing 144 and the third casing 146 of a partitioning member. The sound absorbing member 147 is pressed toward the bottom part of the first casing 144 by the third casing 146, and held within an air passage 142. The third casing 146 is pressed toward a second casing 145 by the elastic force of the sound absorbing member 147, and held within the air passage 142. The sound absorbing member 147 is inserted to the bottom part of the first casing 144, and the first and second casings 144, 145 can be fastened by a snap fit so as to nip the third casing 146. Thus, the manpower for assembling the third casing 146 and the sound absorbing member 147 is reduced.