To eliminate fear of crack and release of a lightweight aerated concrete panel and to process an edge part as well by forming a dense layer having few foams on one or more sides of the lightweight aerated concrete panel as an integrated material.

Oblique line parts in the vicinity of both sides of a panel 1 are dense layers 2 and can be produced by pushing a backplate 8 against the sides of a semihardened panel 4. In the operation, faces of a bottom plate 5, a top plate 6, etc. except faces which are pushed by the backplate, are fixed. The thickness of the dense layers 2 is adjusted by changing the position of the backplate 8. A raw material for a foamed mortar block in a semihardened state, for example, is obtained by blending quartz rock, cement, quick lime and water as main raw materials with gypsum, ground waste, etc., mixing the blend with foams and cutting the resulting material into a panel state to give the semihardened panel 4. The cutting is carried out by using a wire rod such as a piano wire stretched in tension. The whole faces of the obtained semihardened panel 4 are fixed by the backplate and the backplate is pushed against one side to crush foams to form the dense layers 2 on the side parts.