A device for manufacturing a three-dimensional product, which device comprises a work table on which said three-dimensional product is to be built, a powder dispenser which is arranged to lay down a thin layer of powder on the work table for the formation of a powder bed, a ray gun for giving off energy to the powder whereby fusion of the powder takes place, members for controlling of the beam released by the ray gun across said powder bed for the formation of a cross section of said three-dimensional product through fusion of parts of said powder bed, and a controlling computer in which information about successive cross sections of the three-dimensional product is stored, which cross sections build the three-dimensional product, the controlling computer intended to control said members for guiding the ray gun across the powder bed according to a running schedule forming a cross section of said three-dimensional body, whereby said three-dimensional product is formed by successive fusion of successively formed cross sections from powder layers successively laid down by the powder dispenser.