A compressed air engine and a flying object using the engine are disclosed. The flying object includes the following elements. That is, the compressed air engine includes: a top member 11 provided with an air inlet 16; an upper cylinder 12; a lower cylinder 13; a bottom member 14; an air pipe, for passing of a compressed air; a shuttle 20 for performing up/down movements within a cylinder formed by the upper and lower cylinders; and a pair of pistons 21a and 21b over and under the shuttle respectively. The pair of the wings are symmetrically and pivotally assembled to the shuttle and the lower cylinder through securing shafts so as to perform up/down movements in accordance with the up/down movements of the shuttle. A compressed air container 2 is assembled to the bottom of the bottom member, for storing the compressed air.