I'm guessing it's early 90s.
I can't find a serial or any form of ID on it. But even the paint doesn't look like an after-market job, so I'm really confused who made this bike.
Handlebars - Sakae Champion (now Sakae Ringyo)
Handlebar stem - SR (now Sakae Ringyo)
Derailer set - Sun Tour (now Sakae Ringyo)
Cranks - Tourney
Brakes - Dia Compe
Photos tell the rest of the story...