An unmanned aerial vehicle comprising: a housing (110, 220); a wireless communication circuit positioned inside or connected to the housing, wherein the communication circuit is configured to establish wireless communication with an external controller; a plurality of propulsion systems (120, 210) connected to or at least partially embedded in the housing; and a navigation circuit configured to control the propulsion systems, wherein at least one of the plurality of propulsion systems (120, 210) includes: a motor (122, 310) controlled by the navigation circuit; a rotation shaft (320, 520) having an axis extending in a first direction (dl), and including a first end and a second end, wherein the first end is connected to the motor (122, 310), and wherein the rotation shaft (320, 520) is configured to be rotated in a first rotational direction (r) by the motor (122, 310); and a propeller (121, 211-214); and characterized by a cap structure (340, 830) fixed to the second end of the rotation shaft (320, 520); and in that the propeller (121, 211-214) includes: a hub (331, 411) including a through-hole (333, 413) formed in the first direction (dl), such that the rotation shaft (320, 520) rotatably passes through the through-hole; and a plurality of blades (332, 412) connected to the hub (331, 411) in second directions substantially perpendicular to the first direction (dl), wherein the cap structure (340, 830) includes a surface facing toward the propeller (121, 211-214), and at least one spiral recess (1241, 1341) formed in the surface, wherein the hub (331, 411) includes at least one protrusion (414, 533) configured to be slidably engaged in the spiral recess (1241, 1341) when the propeller (121, 211-214) is connected to the cap structure (340, 830), wherein the propeller (121, 211-214) is detachably fixed to or connected to the cap structure (340, 830), such that, when an external force is exerted on at least one of the blades (332, 412), the propeller (121, 211-214) is released from the cap structure (340, 830) to be freely movable along the axis toward the motor (122, 310), and wherein the spiral recess (1231, 1341) extends toward the propeller (121, 211-214) in a second rotational direction opposite to the first rotational direction (r). a housing (110, 220); a wireless communication circuit positioned inside or connected to the housing, wherein the communication circuit is configured to establish wireless communication with an external controller; a plurality of propulsion systems (120, 210) connected to or at least partially embedded in the housing; and a navigation circuit configured to control the propulsion systems, wherein at least one of the plurality of propulsion systems (120, 210) includes: a motor (122, 310) controlled by the navigation circuit; a rotation shaft (320, 520) having an axis extending in a first direction (dl), and including a first end and a second end, wherein the first end is connected to the motor (122, 310), and wherein the rotation shaft (320, 520) is configured to be rotated in a first rotational direction (r) by the motor (122, 310); and a propeller (121, 211-214); and characterized by a cap structure (340, 830) fixed to the second end of the rotation shaft (320, 520); and in that the propeller (121, 211-214) includes: a hub (331, 411) including a through-hole (333, 413) formed in the first direction (dl), such that the rotation shaft (320, 520) rotatably passes through the through-hole; and a plurality of blades (332, 412) connected to the hub (331, 411) in second directions substantially perpendicular to the first direction (dl), a motor (122, 310) controlled by the navigation circuit; a rotation shaft (320, 520) having an axis extending in a first direction (dl), and including a first end and a second end, wherein the first end is connected to the motor (122, 310), and wherein the rotation shaft (320, 520) is configured to be rotated in a first rotational direction (r) by the motor (122, 310); and a propeller (121, 211-214); and characterized by a cap structure (340, 830) fixed to the second end of the rotation shaft (320, 520); and in that the propeller (121, 211-214) includes: a hub (331, 411) including a through-hole (333, 413) formed in the first direction (dl), such that the rotation shaft (320, 520) rotatably passes through the through-hole; and a plurality of blades (332, 412) connected to the hub (331, 411) in second directions substantially perpendicular to the first direction (dl), a hub (331, 411) including a through-hole (333, 413) formed in the first direction (dl), such that the rotation shaft (320, 520) rotatably passes through the through-hole; and a plurality of blades (332, 412) connected to the hub (331, 411) in second directions substantially perpendicular to the first direction (dl), wherein the cap structure (340, 830) includes a surface facing toward the propeller (121, 211-214), and at least one spiral recess (1241, 1341) formed in the surface, wherein the hub (331, 411) includes at least one protrusion (414, 533) configured to be slidably engaged in the spiral recess (1241, 1341) when the propeller (121, 211-214) is connected to the cap structure (340, 830), wherein the propeller (121, 211-214) is detachably fixed to or connected to the cap structure (340, 830), such that, when an external force is exerted on at least one of the blades (332, 412), the propeller (121, 211-214) is released from the cap structure (340, 830) to be freely movable along the axis toward the motor (122, 310), and wherein the spiral recess (1231, 1341) extends toward the propeller (121, 211-214) in a second rotational direction opposite to the first rotational direction (r).