To provide a novel technique in hydraulic bulging, which is suitable for performing super plasticity phenomena.

A hydraulic bulging apparatus comprises a lower die 1 having a concave forming portion 10 formed therein so as to face to the lower surface of a workpiece 3, an upper die 2 which grips the workpiece 3 between the lower die 1 and the upper die 2 and has a pressurizing chamber 4 formed therein so as to face to the upper surface of the workpiece 3, heating means 7, 7 for heating the workpiece 3 up to a required temperature at which the characteristic of the super-plasticity can be achieved, a pressurizing metal which melts at a temperature nearly equal to the required temperature described above and exists in a liquid state, a reservoir tank 5 for preserving the pressurizing metal in the liquid state, a molten metal supplying means 6 for press-feeding the pressurizing metal existing in the reservoir tank 5 to the pressurizing chamber 4, and a controlling means 8 for controlling the operation of the molten metal supplying means 6. The hydraulic bulging is performed by using the hydraulic bulging apparatus.