According to one embodiment, a light detector includes an element, and a structure body. The element includes a first semiconductor region, a second semiconductor region, and a third semiconductor region. The second semiconductor region is provided on the first semiconductor region. The third semiconductor region is provided on the second semiconductor region. The structure body is provided around the element. The structure body includes first and second insulating portions and a metal-including portion. The metal-including portion is provided above the first insulating portion. A position in the first direction of a portion of the metal-including portion is same as a position in the first direction of the third semiconductor region. The second insulating portion is positioned between the metal-including portion and the element in the first plane. A thickness of the first insulating portion is greater than a thickness of the second insulating portion in the first plane.