a semiconductor substrate that has a first main surface and a second main surface opposed to the first main surface;

an epitaxial layer in the semiconductor substrate;

a first semiconductor layer that is of a first conductivity type, and included in the semiconductor substrate and closer to the first main surface than to the second main surface;

a multiplication region included in the epitaxial layer, and causes avalanche multiplication to a charge generated in the semiconductor substrate through photoelectric conversion, the multiplication region comprising at least two multiplication regions; and

an isolation region that separates the at least two multiplication regions,

wherein a gradient of an impurity concentration distribution of the epitaxial layer includes a first section where an impurity concentration of the epitaxial layer is substantially constant and a second section where the impurity concentration drastically increases from the first main surface toward the second main surface, the second section following the first section.