A casted ingot of a heat treatment type Al—Zn—Mg series aluminum alloy comprising Zn: 4.0-8.0% by mass, Mg: 0.5-2.0% by mass, Cu: 0.05-0.5% by mass, Ti: 0.01-0.1% by mass, and any one or more of Mn: 0.1-0.7% by mass, Cr: 0.1-0.5% by mass and Zr: 0.05-0.3% by mass, and the balance being aluminum and incidental impurities is extruded at a homogenization treatment temperature after a homogenization treatment without cooled, and a resulted extruded material is die quenched at a cooling rate equal to or more than 100° C./min and then subjected to an artificial aging treatment, wherein the homogenization treatment is carried out by heating to the homogenization treatment temperature as 430-500° C. at a heating rate less than 750° C./hr or by heating to the homogenization treatment temperature and held the homogenization treatment temperature for 3 hours.