PURPOSE: To accelerate the dehydration of a slurry without bringing about the scaling-up of a production line in producing a plate-shaped building element by a flow-on system.

CONSTITUTION: In an apparatus for producing the green panel of a plate-shaped building element constituted so that a sheet 3 having water permeability is provided so as to be capable of advancing in its longitudinal direction and a hopper 6 supplying a slurry to the upper surface of the sheet 3 is provided above the sheet 3 and a suction means 4 dehydrating the slurry under reduced pressure is provided to the lower surface of the sheet 3, a vibrator 27 applying vibration to the slurry supplied to the upper surface of the sheet 3 is provided to the section S where the suction means 4 performs dehydration under reduced pressure.