To provide a stack forming device for stacking a sheet-like product at small cost in a small required space.

This stack forming device is constituted so that a paper product 12 is supplied to a transfer area 32 by a feeding conveyor 28. This device has a plurality of placing tables 42 having respectively a placing surface 40 for a stack 10 of the supplied product. The placing tables 42 move along a circulating passage-like table circulating passage 68, and have flexibility in partial segment. Thus, the placing tables 42 can be adapted to a shape of curved parts 99, 102, 116 and 130 of the table circulating passage 68 in the partial segment and a small area, and can be guided in the curved parts 99, 102, 116 and 130 from its front side 94. The stack 10 of the paper product 12 is carried away from a sending-out area 46 by a taking-out conveyor 48.