To improve working efficiency by simultaneously lowering an upper die base and advancing a following body in the center direction through a straight guide cam mechanism in a hydraulic bulge device.

In a hydraulic bulge device A1, a clamping part K1 is provided with a pair of cam driver 11 provided on an upper die base 2 in a suspended manner, a guide rod to lower the upper die base 2, and an upper die holder 4 arranged on a lower tip of the guide rod in a suspended manner. The hydraulic bulge device is provided with a stock tube feed part S1 having a roller arranged on a side part of a piston of a stock tube feed cylinder 10 of a following body which is moved in the right-to-left direction in an abutting manner on a cam driver 11 to be lowered as the upper die base 2 is lowered.