It is provided a lens unit to be small-sized, while reducing deterioration in optical performance after experiencing thermal expansion. The lens unit includes an aperture member, a lens, an image sensor, and a holder. A range where the aperture member abuts on a flange part of the lens overlaps with a range where the holder abuts on the flange part of the lens. A first gap is provided between a holder inclined surface of the holder and a lens inclined surface of the lens over the entire circumference. A second gap is provided between an outer circumferential surface of the lens and an inner surface of the holder over the entire circumference.