PURPOSE: To enhance the usage efficiency of a formwork and also to reduce the number of fittings for holding an original sheet by inserting a partition member which has height lower than the side wall of a formwork into this formwork and forming the original sheet made of concrete having a groovelike recess and thereafter cutting the original sheet in the groovelike recess to separate it into a plurality of panels.

CONSTITUTION: The partition members 4 having the dimension of height lower than the side walls 1B - 1E by height H are inserted into the inside of a formwork 1. The projections 5 are inserted into the suitable holes 2 of the bottom part of the formwork. Then bolts 7 are screwed into the holes 3 provided in the positions correspondent to the partition members 4 of the side walls 1B and clamped. Thereby the partition members 4 are positioned and arranged in the formwork 1. Three pieces of space 10 - 12 for forming a panel are provided. Arrangement materials 13 of reinforcement are hung and held in these spaces and thereafter concrete slurry is placed in the formwork 1 to the level higher than the partition members 4. After slurry is coagulated, an original sheet 14 is obtained by separating the formwork. This original sheet 14 has the same size as the formwork 1. The groovelike recesses 15 are formed in the parts of the partition members 4 and become the connection parts 16. The original sheet 14 is aged in an autoclave and thereafter cut in the groovelike recesses 15. Thereby three pieces of separated panels are manufactured.