Disclosed is a noise reduction device wherein a microjet ring (16) having a plurality of injection tubes (26) arranged at an equal distance apart in the circumferential direction, is provided on the injection-side peripheral edge of the cylindrical partition wall of a jet engine; and a supply path through which a part of compressed air is introduced from a passage located upstream of a combustor within an jet engine to the plurality of injection tubes (26), is provided, so that part of the compressed air is injected toward the jet stream through the injection tubes (26).