A light detection device detects an incident position of light. The plurality of pixels are arranged two-dimensionally in a matrix and individually have a first photosensitive portion and a second photosensitive portion. The first circuit connects a plurality of first photosensitive portions to each other for every row. The second circuit connects a plurality of second photosensitive portions to each other for every column. The first reading unit reads signal data through the first circuit. The second reading unit reads signal data through the second circuit. The first circuit includes row switches arranged to switch electrical connection and disconnection between first photosensitive portions adjacent to each other in the same row.