PURPOSE: To produce a panel type heat radiator of high reliability against oil leakage or the like in a short time by sandwiching the outside circumferential end parts of two sheets of press-formed panel plates with guide rollers from above and below, moving these in tight contact with each other and welding the tight contact parts by means of a laser.

CONSTITUTION: The outside circumferential parts of two sheets of panel plates 2 are sandwiched with guide rollers 3 from above and below, whereby their end parts are brought into tight contact with each other. A laser condenser 4 is so adjusted that the laser is focused to the tight contact parts thereof and while the tight contact parts are moved along the outside circumferential end parts of the panel plates 2, the outside circumferences of the plates 2 are welded by the laser. A panel element is formed in this way, and plural pieces of such elements are connected to constitute a panel type heat radiator.