A rust on Rubus idaeus (Raspberry). There is no host-plant alternation, and this is not considered to be a gall-causer.  Yellow aecia are on leaf uppersides; yellow uredinia and black telia on undersides. 

Similar species affect brambles (Rubus fruticosus, etc.)

host

Photograph both sides of the leaf.  Ensure you have noted the host-plant species in your comments

Raspberries