PURPOSE: To obtain an original material with homogeneous density by controlling the thickness and the dehydration speed of a slurry cast into a mold to a constant level in the cast molding of a pressurized slurry.

CONSTITUTION: When a pump 3 for delivering a slurry under pressure is operated at a preset delivery speed by driving a motor 8 forward while the slurry 2 in a slurry tank 1 is fed into the pump 3, the slurry 2 passes through a pipe 15 for sending the slurry under pressure to be delivered to and cast into a casting mold cavity 14. When pressure in the pipe 15 increases to a predetermined level in consequence that the cavity 14 is filled with the slurry 2, a pressure sensor 16 detects this increase in pressure, whereby the counting by a timer 25 in controller 21 is started and the process of controlling the slurry to be cast under pressure is started according to a control program preset in a CPU 22 in the controller 21. In this case, simultaneously, a change-over valve connected to a vacuum source is opened, and vacuum dehydration in a mold 11 is forcibly carried out.