PURPOSE: To provide a ream divider device for a flat paper sheet by which the ream of flat paper sheets piled in heaps can be mechanically divided without injuring the paper face of the ream.

CONSTITUTION: This ream divider device is constituted of a marker presser roll l, a marker sucking member 2, a divider pad 3, a divider belt 4, a belt inserting bar 5, a reel drum 6, and a tacker 7, and the divider belt 4 can be advanced or retreated in X-axis direction, the tacker 7 can be moved in X-axis, Y-axis, Z-axis directions, the marker M on the end edge part of the ream is pressed by the marker presser roll 1, the marker M is sucked and removed by the marker sucking member 2, the ream on the upper part of the marker M is lifted by the divider pad 3, and the divider belt 4 is inserted into the space part so as to divide the ream. After inserting the tacker 7 into the end edge part of the ream through the divider belt 4, it can be moved along the end edge part of the ream in the Y-axis direction, and the ream can be divided in the optional position so as to form a space part.