To employ a recyclable packing material for a form device.

This packing material is a band-like rectangular parallelepiped- shaped elastic body 30, one side of which acts as a fitting surface and the other side of which as an abutting surface 30b. A recessed bead groove 32 is formed at the almost middle of the abutting surface. In addition, in the interior of the elastic body, a hollow part is formed. A packing material, in which an elastic part 35 is composed of the hollow part and the recessed bead groove, is employed. On the abutting portion of the steel plate 15 for an inner form, a fitting recessed bead part 24 is formed. The fitting surface of the packing material is fitted to the fitting surface of the packing material. Under the state that some part of the abutting surface of the packing material is slightly projected above the abutting portion, the steel plates 13 and 15 are pressed against each other, an internally filled matter is packed. Since the elastic body has the elastic part, when demolded, the packing material restores its original shape. As a result, the recycling of the packing material can be realized.