A light detector is configured such that a light receiving portion having APDs and a peripheral circuit portion are provided on a first principal surface of a p-type semiconductor substrate, and further includes a back electrode provided on a second principal surface of the semiconductor substrate and a p-type first separation portion provided between the light receiving portion and the peripheral circuit portion. The APD has, on a first principal surface side, an n-type region and a p-epitaxial layer contacting the n-type region in a Z-direction. The peripheral circuit portion has an n-type MISFET provided at a p-well and an n-well provided to surround side and bottom portions of the p-well.