PURPOSE: To reduce radio wave reflection without decreasing flight performance.

CONSTITUTION: In the inside of a duct 3, leading to a front face of engines 4 from an air intake port 2 opened to the front of an aircraft 1 to which two sets of the engines are mounted, a partitioning plate 5 for dividing this duct 3 into two air paths is provided. The partitioning plate 5 is 180° twisted about an airframe axis, to flow air, advanced in from a right side of the partitioning plate 5 relating to the air intake port 2, into the left side engine and air, advanced in from a left side of the partitioning plate 5, into the right side engine. Since the partitioning plate 5 is 180° twisted about the airframe axis, the engine 4 can not be seen from the front of the air intake port 2. Accordingly, even a threat radio wave, entered the air intake port 2, is interrupted by the partitioning plate 5 or an internal wall of the duct 3 and prevented from directly reaching the front face of the engine of easily reflecting the radio wave.