A multiple-winding pipe forming device for forming a wound pipe, the multiple-winding pipe forming device comprising: a plurality of pairs of forming rollers arranged along a feeding direction of a metal sheet that is an object of forming, each pair of forming rollers opposing one another so as to sandwich, in use, the metal sheet, and the plurality of pairs of forming rollers being configured to curl the metal sheet and to wind the metal sheet into a roll shape; and a mandrel fabricated of metal, the mandrel including: a shaft that extends in the feeding direction and is disposed, in use, inside the metal sheet wound in the roll shape, one end side of the shaft being retained, which one end side is disposed upstream in the feeding direction, and a working portion (28, 62) provided at an opposite end side of the shaft from a side thereof at which the one end side is disposed, the working portion (28, 62) including a taper portion (28A, 62A) that increases in diameter from upstream to downstream in the feeding direction, wherein the taper portion (28A, 62A) of the working portion (28, 62) is disposed, in use, at a position at which the metal sheet wound in the roll shape is sandwiched by, of the plurality of pairs of forming rollers, a pair of the forming rollers that is disposed at a downstream side in the feeding direction, characterized in that the multiple-winding pipe forming device further comprises a moving apparatus that moves the mandrel along the feeding direction, the moving apparatus including: a retention portion that retains the one end side of the shaft and is movable to an upstream side and the downstream side in the feeding direction, a drive source that moves the retention portion, a sensor that, via the retention portion, detects tension acting on the shaft, a control section that, in accordance with a tension detected by the sensor, controls the drive source and adjusts a position of the retention portion along the feeding direction; a position of the mandrel along the feeding direction is controlled by the moving apparatus such that the taper portion (28A, 62A) of the working portion is disposed at the nipping portion of the pair of forming rollers. a plurality of pairs of forming rollers arranged along a feeding direction of a metal sheet that is an object of forming, each pair of forming rollers opposing one another so as to sandwich, in use, the metal sheet, and the plurality of pairs of forming rollers being configured to curl the metal sheet and to wind the metal sheet into a roll shape; and a mandrel fabricated of metal, the mandrel including: a shaft that extends in the feeding direction and is disposed, in use, inside the metal sheet wound in the roll shape, one end side of the shaft being retained, which one end side is disposed upstream in the feeding direction, and a working portion (28, 62) provided at an opposite end side of the shaft from a side thereof at which the one end side is disposed, the working portion (28, 62) including a taper portion (28A, 62A) that increases in diameter from upstream to downstream in the feeding direction, wherein the taper portion (28A, 62A) of the working portion (28, 62) is disposed, in use, at a position at which the metal sheet wound in the roll shape is sandwiched by, of the plurality of pairs of forming rollers, a pair of the forming rollers that is disposed at a downstream side in the feeding direction, a shaft that extends in the feeding direction and is disposed, in use, inside the metal sheet wound in the roll shape, one end side of the shaft being retained, which one end side is disposed upstream in the feeding direction, and a working portion (28, 62) provided at an opposite end side of the shaft from a side thereof at which the one end side is disposed, the working portion (28, 62) including a taper portion (28A, 62A) that increases in diameter from upstream to downstream in the feeding direction, wherein the taper portion (28A, 62A) of the working portion (28, 62) is disposed, in use, at a position at which the metal sheet wound in the roll shape is sandwiched by, of the plurality of pairs of forming rollers, a pair of the forming rollers that is disposed at a downstream side in the feeding direction, characterized in that the multiple-winding pipe forming device further comprises a moving apparatus that moves the mandrel along the feeding direction, the moving apparatus including: a retention portion that retains the one end side of the shaft and is movable to an upstream side and the downstream side in the feeding direction, a drive source that moves the retention portion, a sensor that, via the retention portion, detects tension acting on the shaft, a control section that, in accordance with a tension detected by the sensor, controls the drive source and adjusts a position of the retention portion along the feeding direction; a retention portion that retains the one end side of the shaft and is movable to an upstream side and the downstream side in the feeding direction, a drive source that moves the retention portion, a sensor that, via the retention portion, detects tension acting on the shaft, a control section that, in accordance with a tension detected by the sensor, controls the drive source and adjusts a position of the retention portion along the feeding direction; a position of the mandrel along the feeding direction is controlled by the moving apparatus such that the taper portion (28A, 62A) of the working portion is disposed at the nipping portion of the pair of forming rollers.