A grid electrode, disposed along a corotron wire, includes a planar, plate-shaped member having plural openings in each of which a longitudinal direction and a short side direction are formed, the longitudinal directions of the respective openings being lined up to be in a same direction, and connecting portions connecting openings adjacent to each other in a opening longitudinal direction and connecting portions connecting openings adjacent to each other in a opening short side direction. At each opening, a shortest distance from a center point to an opening edge is less than 1.5 mm, a grid opening ratio is greater than or equal to 82%, and a length of the longitudinal direction is at least 1.3 times a length of the short side direction. The connecting portions connecting openings adjacent to each other in the opening longitudinal direction are not disposed on a same line which is orthogonal to the corotron wire.