A folding stepstool, comprising: a top board extending in a first direction and in a second direction orthogonal to the first direction, the top board including: a first top board of which back surface is formed having a recessed first space, a second top board of which back surface is formed having a recessed second space, the second top board being arranged side by side with the first top board in the first direction, and a hinge that pivotally connects the first top board and the second top board so that back surfaces of the first top board and the second top board get closer to each other, a first leg portion (20L, 30L) provided at a first end in the second direction of a back surface of the top board, the first leg portion having a first leg disposed at the back surface of the first top board and a second leg disposed at the back surface of the second top board, a first slide rail provided at the first end in the second direction of the back surface of each of the first top board and the second top board, the first slide rail extending in the first direction to support the second leg so that the second leg is slidably movable to the back surface of the first top board, a second leg portion (20R, 30R) provided at a second end in the second direction of the back surface of the top board, the second leg portion having a third leg disposed at the back surface of the first top board and a fourth leg disposed at the back surface of the second top board, a second slide rail provided at the second end in the second direction of the back surface of each of the first top board and the second top board, the second slide rail extending in the first direction to support the third leg so that the third leg is slidably movable to the back surface of the second top board, wherein the first leg and the second leg are configured to be accommodated in the first space of the first top board in a state where the first leg and the second leg are positioned on the back surface of the first top board, the third leg and the fourth leg are configured to be accommodated in the second space of the second top board in a state where the third leg and the fourth leg are positioned on the back surface of the second top board, and the top board is configured to be pivotable so that the back surfaces of the first top board and the second top board get closer to each other in the state where the first leg and the second leg are accommodated in the first space of the first top board and in the state where the third leg and the fourth leg are accommodated in the second space of the second top board. a first top board of which back surface is formed having a recessed first space, a second top board of which back surface is formed having a recessed second space, the second top board being arranged side by side with the first top board in the first direction, and a hinge that pivotally connects the first top board and the second top board so that back surfaces of the first top board and the second top board get closer to each other, a first leg portion (20L, 30L) provided at a first end in the second direction of a back surface of the top board, the first leg portion having a first leg disposed at the back surface of the first top board and a second leg disposed at the back surface of the second top board, a first slide rail provided at the first end in the second direction of the back surface of each of the first top board and the second top board, the first slide rail extending in the first direction to support the second leg so that the second leg is slidably movable to the back surface of the first top board, a second leg portion (20R, 30R) provided at a second end in the second direction of the back surface of the top board, the second leg portion having a third leg disposed at the back surface of the first top board and a fourth leg disposed at the back surface of the second top board, a second slide rail provided at the second end in the second direction of the back surface of each of the first top board and the second top board, the second slide rail extending in the first direction to support the third leg so that the third leg is slidably movable to the back surface of the second top board, wherein the first leg and the second leg are configured to be accommodated in the first space of the first top board in a state where the first leg and the second leg are positioned on the back surface of the first top board, the third leg and the fourth leg are configured to be accommodated in the second space of the second top board in a state where the third leg and the fourth leg are positioned on the back surface of the second top board, and the top board is configured to be pivotable so that the back surfaces of the first top board and the second top board get closer to each other in the state where the first leg and the second leg are accommodated in the first space of the first top board and in the state where the third leg and the fourth leg are accommodated in the second space of the second top board.