It is an "autoportrait" selftimer with a curved mirror. After setting the timer, the photographer goes to his place and he can see his own reflection in the mirror.
Known numbers:
2817____Michel's collection.
4314____David Tomlinson.
4881____Jacques collection.
5086____PYC. collection.
5752____seen on eBay.
8083-------imcphoto collection
9944____Bill Parkinson collection
11508___seen on eBay.