A charging device has a sheet electrode with triangular pins aligned in a first direction and a cleaner unit for cleaning the sheet electrode while moving in the first direction and in a second direction opposite to the first direction. The cleaner unit has a grinding member for grinding the sheet electrode, a first collecting member, which is disposed downstream in the first direction from the grinding member, for collecting extraneous matter, a second collecting member, which is disposed downstream in the second direction from the grinding member, for collecting extraneous matter, and a switching section for changing a contact state of the first collecting member with the sheet electrode and a contact state of the second collecting member with the sheet electrode. While the cleaner unit is moving in the first direction, the second collecting member is pressed against the sheet electrode with greater force than the first collecting member is pressed against the sheet electrode, and while the cleaner unit is moving in the second direction, the first collecting member is pressed against the sheet electrode with greater force than the second collecting member is pressed against the sheet electrode.