An unmanned aerial vehicle according to the present invention may comprise: a rotor-blade for providing thrust according to generation of main stream; and a safety guard disposed to surround the rotor-blade. The safety guard may comprise: a guide member which is disposed coaxially with the rotor-blade while having a gap between the guard member and the end of the rotor-blade, so as to stabilize, when the rotor-blade rotates, a flow field suctioned by a negative pressure, and stably boost a discharge flow when the pressure is changed to a positive pressure; and a diffuser which is disposed coaxially with and radially spaced apart from the guide member, and generates a secondary flow toward the main stream to increase a flow rate.