Jang has shown considerable improvement in recent weeks with top tens in each of his last three starts worldwide in both Japan Tour and OneAsia Tour events.
Jang, who lead by two heading into the final round, appeared to have the event in safe keeping until struggles early in his back nine saw the margin reduced to just one with two holes to play.
Birdies at his final two holes however saw the Korean home by three.
Jang's victory also earned him a start at the Open Championship this year with the first four players in this event and inside the top twelve not otherwise qualified for Royal Liverpool have played their way to a start in the third major of the year in July.
The other three players to now be starters at the Open via this event are Pagunsan, Hyung Tae Kim and Tomohiro Kondo.
The leading Australasian in this week's event was New Zealander Michael Hendry who finished in a share of 6th with Kurt Barnes 13th and Steve Conran 17th.
The Japan Tour will now play their Japan PGA Championship at the Golden Valley Golf Club in Hyogo Prefecture.