To provide an ultrahigh pressure generating device capable of precisely measuring an amount of a lateral anvil moved even when a guide block is deformed and pressurizing a pressure medium while maintaining it to a predetermined shape.

In the DIA type ultrahigh pressure generating device provided with a pressurizing space PA compressing by pressure a pressure medium, an annular base plate 30 is arranged on the upper surface of a lower guide block 1 so as to enclose the peripheral of a plurality of sliding blocks 7, a plurality of detecting sensors 35 for the amount of migration which detects the amount of migration of the plurality of lateral anvils 11c are installed on the base plate 30, and the base plate 30 is arranged so that its center may be located on the center axis CL of the ultrahigh pressure generating device, and is so arranged that relative movement to the lower guide block 1 in a radius direction of the base plate 30 is of not-fixed state but that relative movement of the lower guide block 1 in the circumference of the base plate 30 is of a fixed state.