To prevent a product from being cracked by a method wherein in a state that mutually opposed two faces adjoining to a face to be patterned are restricted by applying a backplate thereto, the backplate or a template having a pattern is applied to a face opposed to the face to be patterned, and they are pressed.

A block 1 is vertically restricted, and a lateral backplate 5 is allowed to abut against a block 1 by a hydraulic cylinder 3. In this state, a lateral template 4 is pushed into the block 1 by the hydraulic cylinder 3, and an uneven pattern is formed laterally on the block 1. Then, in a state that the lateral template 4 is pushed into the lightweight cellular concrete block 1, and in a state that a lateral backplate 5 is allowed to abut against the block 1 to restrict the block laterally, a base plate 2 is transferred to a second station. Thereafter, an upper side template 7 is allowed to descent by a lifting hydraulic cylinder 9, the template is pushed into the block 1, and an uneven pattern is formed even on the upper face of the lightweight cellular concrete block 1.