This is an early example of a chainstay mounting SunTour Wide derailleur manufactured for SunTour by a company called Iwai. The small enamel badge riveted on just below the frame mounting screws says ‘SunTour Iwai’.
The underlying design remains a version of any number of French designs from the 1930’s (see the Super Champion/Osgear Grand Sport) . As ever, though, this Suntour is a well executed example of the genre. The cutaway mounting plate is particularly stylish.