To provide a hydroforming device and process which can mold an untreated pipe at a large expansion rate.

The invention relates to the hydroforming device 2 which molds an expanded section 52a in a part of the untreated pipe 1 held in a mold 4 (11), with a fluid pressure given to the inside of the untreated pipe 1. In the mold 4, recesses 14 are formed to partition spaces which are larger than the expanded section 52a. In the recesses 14 provided are rotary inserts 5 of which the molding faces 25 are gradually sloped from the position where the formation commences to the position where the formation finishes.