PURPOSE: To manufacture an extruded material with a difference in thickness and free from a bend by cutting it after heating and softening treatments after butting the thin parts of a pair of extruded materials with a difference in thickness, having a thick part on one side of a thin part as one body and after extruding the extruded materials symmetrically coming into contact with each other as one body.

CONSTITUTION: After butting the thin parts of a pair of extruded materials 3 with a difference in thickness, having a thick part 2 on one side of a thin part 1 as one body and after extruding temporary extruded materials 4 symmetrically coming into contact with each other as one body, heating and softening treatments are performed to this temporary extruded material 4. Next, this temporary extruded material 4 is cut at a contact part 5 where the thin parts are butted. Consequently, a strain on the temporary extruded material 4, is removed by performing the heating and softening treatments. And, even if the temporary extruded material 4 is cut at the contact part 5 where the thin parts are butted, a bend does not occur, and the extruded material 3 with a difference in thickness, can be manufactured to a straight extruded material.