To stabilize intake inner flow by arranging many air extracting holes on a part continued to a supersonic ramp in a flow passage forward a throat of a supersonic intake, and arranging a slide plate on a boundary between a port for communicating many air extracting holes with an outside of the intake and an outside of the intake.

Many holes 9' for extracting air having a large capacity are disposed in a supersonic intake 1' and on a part continued to a supersonic ramp 7 in a flow passage forward a throat 3, and those holes 9' are communicated with an outside of an intake and one large communicating port 10. A slide plate 11 is disposed on a boundary between the communicating port 10 and an outside of the intake. The slide plate 11 is held in a condition in which an opening body 12 of the communicating port 10 is opened by a hook 15. When pressure change in which a pressure sensor 19 is a constant value or more is detected, a solenoid magnet 17 is excited to release lock of the hook 15 so as to slide an opening end 12 in the closing direction by a coil spring 14.