To stack sheets in a plurality of conveying passages without making a device large in size.

In the sheet stacking device, when the sheet P1 is conveyed to a first conveying passage and the sheet P2 is conveyed to a second conveying passage, a control part 32 upwardly moves ride-up members 18A-18C and stoppers 19A-19C. Subsequently, the control part 32 moves a movement member 17B in a direction of a groove B by circulating/moving movement belts 16B, 16C and moves a movement member 17C in a direction of a groove C. Thereby, the movement members 17B, 17C move the sheet P1 in a direction of the ride-up members 18B, 18C. The sheet P1 is moved along inclination parts 180 of the respective ride-up members, rides over the ride-up members 18B, 18C and covers the sheet P2. After the sheet P1 rides over the ride-up members 18B, 18C, when the movement members 17B, 17C are moved to a position contacted with a member 11A, the sheet P1 is stacked on the sheet P1.