To provide a radiator, for an electric apparatus, in which respective panels can be aligned easily and precisely in their assembling operation, in which a pitch between the panels can be kept with good accuracy, in which thin plates are welded easily, in which the strength of a welded joint part is increased, whose quality can be enhanced and which has a design tolerance.

Header parts 2 which are to be used as passages for a coolant are molded at panel plates 1 so as to be cylindrical. Two panel plates 1 are combined to be shell-shaped in such a way that the header parts 2 are directed outward. Their circumferences are seam-welded, panels 3 are formed, rings 6 in which protrusion parts 7 have been formed at the outside in central parts in the axial direction and whose cross section is protrusion-shaped are inserted into welded parts 4 at the header parts 2 of the panels 3 in such a way that the header parts 2 are situated on both sides of the protrusion parts 7. The rings 6 and the header parts 2 at the panels 3 are welded, the panels 3 in the required number are connected sequentially, and a radiator 5 is constituted.