All aluminum alloy ultrahigh vacuum system of a beam transport line (350 m long) from 2.5 GeV linac to TRISTAN accumulation ring was completed. Vacuum beam ducts, bellows, fittings, flange/gasket/bolt, nut and washer combinations, feedthroughs, gauges, windows, ion pumps, turbomolecular pumps, all metal valves and related ultrahigh vacuum components are all aluminum alloys. Vacuum beam ducts are joined by fully automatic welding without flanges. The vacuum system is divided by gate valves into 12 sections. Each section is provided with a 30 l/s ion pump and a 50 l/s non-evaporable getter. Base pressure is in the range of 10-6 Pa without baking. Pressure rise due to beam is negligible. Estimated outgassing rate after 11 month evacuation without baking is 6 × 10-9 Pa·m3/s·m2 for the specially extruded beam ducts. The present system satisfied conditions such as high performance, high reliability, simplicity, small size, light weight, low residual radioactivity and low cost.