A sheet fed from an image forming device to a path carry-in port is guided to a first accumulating section along a straight path or guided to a second accumulating section along a branch path branched from the straight path. A buffer path section is formed so as to make the sheet temporarily stay between a first sheet discharge roller pair disposed on the straight path side of the branch path at a position downstream of a branch portion and a second sheet discharge roller pair disposed in the branch path. The sheet staying in the buffer path section is conveyed to the first accumulating section by rotation of the first and second conveying rollers in one direction and to the second accumulating section by rotation of the first and second conveying rollers in an opposite direction to the one direction.