A photodetecting device is provided. The photodetecting device includes an array substrate. The first scan line extends in a first direction. The first data line extends in a second direction, wherein first data line is crossed with the first scan line. The first electronic unit is electrically connected to the first scan line and the first data line. The second electronic unit is adjacent to the first electronic unit and is disposed along the first direction. The third electronic unit is adjacent to the first electronic unit and is disposed along the second direction. The common line transmits a signal to the first electronic unit, the second electronic unit and the third electronic unit. The common line is disposed between the first electronic unit and the second electronic unit, or between the first electronic unit and the third electronic unit.