An optical unit includes a first lens, a diaphragm, a second lens, a third lens, a fourth lens, and a fifth lens. The first lens is a positive meniscus lens which is convex toward an object side. The second lens has a positive power. The third lens has a negative power. The fourth lens has a positive power. The fifth lens has a negative power. Those are arranged in the stated order from the object side to an image plane side.