A lens unit is provided that includes: a first lens that is housed inside a lens-barrel, the first lens including a first lens section and a first flange section that juts out from the first lens section in a direction orthogonal to an optical axis direction; a second lens that is housed inside the lens-barrel further toward an imaging plane side than the first lens, the second lens including a second lens section and a second flange section that juts out from the second lens section in a direction orthogonal to the optical axis direction; and a spacing ring that is sandwiched between the first lens and the second lens and that defines a spacing between the first lens and the second lens, the spacing ring includes a main body disposed between the first flange section and the second flange section in the optical axis direction, first protrusion portions that protrude in the optical axis direction from an object side of the main body, and second protrusion portions that protrude in the optical axis direction from the imaging plane side of the main body and are disposed offset with respect to the first protrusion portions when projected along the optical axis direction.