To apply working of not only punching and bulging but cutting/raising or the like.

In a hydroforming die 20 in which: a cavity for housing a workpiece 11 having a closed cross section is formed on the die body 21; a slide hole 26 which is communicated with the cavity 28 is formed on the die body 21; a sliding tool 27 which is slidably fit to this slide hole 26 is provided; the workpiece 11 is housed in the cavity 28; working fluid is filled up in the workpiece 11 and, by pulling out the sliding tool 27 to the outside of the die body 21 after the inside of the workpiece 11 reaches a prescribed internal pressure, punching is applied to the workpiece 11, a curved surface part (round part) 35 for partially obstructing breaking is provided in the end part on the side of the workpiece 11 of the slide hole 26.