I tend to agree with Jemoryl. Piaggio was the corporation that owned Bianchi and Vespa in the early 1980s. The Piaggio decal appeared on the seat tube of all the models for a short period. There may also have been a Piaggio model, but I'm not aware of it.
The serial number will indicate if it is an Italian or Japanese frame and also indicate the year (if it is Italian). An Italian built frame will have a part two serial number on both sides of the seat lug or on the bottom bracket. Japanese frames have a single serial number on the bottom bracket. Of course, the bottom bracket threading is another way to determine the origin, with Japanese frames being English (1.370" x 24 TPI) and the the Italian frames having Italian threading (36mm x 24 TPI).