Our first thought was BMW 315/1 Roadster, but it's just not close enough. For the czech made Aero Roadster counts the same. A prototype or a rebody of either of these two maybe? Or are we looking in the wrong direction? Should we go to France for research. Or to the United Kingdom after all? Who will step forward and bring light in this roadster matter.
Update by editor: well this one didn't last long (minutes!) thanks to Bartosz Cieluch. In fact we should have known! It's an Adler Trumph Junior roadster around 1934.