A flattening roller (38) is supported on horizontal guides (32, 34) and rolls alternately in opposite directions along the guides. A tray (30) is arranged horizontally between the guides, and is progressively lifted to approach to the cylindrical surface of the roller. The tray turns by a quarter turn around a vertical axis at the end of each stroke of the roller along the guides. A lump of dough placed on the tray is progressively flattened to a thin, round shape.