There are provided a lens unit, a camera system, and an elastic member that can prevent an annular elastic member from being entangled. The lens unit includes an optical system that includes at least one lens, a lens barrel that receives the optical system, a lens mount that is provided on one end side of the lens barrel and includes a plurality of bayonet claws, and an annular elastic member that is mounted on the lens mount. The elastic member includes a protruding portion that is positioned on the one end side and protrudes inward in a radial direction, and a dent that is positioned on an outer peripheral side opposite to the protruding portion so as to be closer to the other end side than the protruding portion.