PURPOSE: To reduce noises by constructing a machine room including a compressor therein in a closed state thereof leaving a heat dissipation opening part, setting the size in one direction among three-dimensional sizes in the machine room larger than the other, and further closing a cover of a heat dissipation opening part and interrupting active control.

CONSTITUTION: A machine room 17 is constructed into an enclosed state leaving a heat dissipation opening part 21a as it is, and a size in one direction among three-dimensional sizes in the machine room 17 is set larger than the other sizes. Thereby, the title device is constructed so that only a primary mode is existent in a frequency range or less where a standing wave of a sound in the machine room 17 is to be cancelled out. Further, a cover 22 free to be opened and closed is provided on the heat dissipation opening part 21a. Further, control means 37 is provided to close the cover 22 for a predetermined time upon starting a compressor 18, and interrupt the sound deadening operation by a controlling sound generator 25. Active control is simplified and control accuracy is improved, while even noise difficult to be actively controlled upon starting the compressor can be prevented from leaking to the outside.