PURPOSE: A header of heat exchanger is provided to have a cover part sufficiently stand against external force such as hydraulic pressure. CONSTITUTION: A header includes a pipe(30) acting as a passage for water; an insertion part(10) shaped in platy rod form and having a pipe insertion hole(11) formed for the pipe to be inserted therein; and a cover part(20') shaped in rod form and a having semicircular section with one side open and a connecting part(21') with both ends bending inwardly in L-shape to be coupled to the insertion part inserted from an upper side or a lower side. External force is applied on a body of the cover part instead of the connecting part thereby.
