You will find here hundreds of frogs, of all sizes, made from all kind of materials, from functional articles to ornaments and lucky charms... The explanation is a wordplay: since the street runs along a small river, there are certainly a lot of frogs here, and in Japanese kaeru means "frog" but also means "return" - so the frogs are good at returning things in your possession - money for example...
Since the whole street is themed with frogs, there are also several frog statues decorating the area and in this photo you can see the most spectacular of them, made from fiberglass by the students of the Tokyo University for Arts. Although it is huge and brightly colored, I almost missed it: I visited Matsumoto in a festival day, so besides the regular shops the street was filled with festival food stalls and the statue was somewhere in the back... It represents two fierce-looking samurai frogs fighting with katana in their hands:
EXIF info:
Nikon D90
Lens: 8-16mm F/4.5-5.6G
Focal Length: 11mm
Aperture: F/7.1
Shutter Speed: 1/100s
ISO Sensitivity: ISO 200