I walked past this machine every weekday for a year without noticing it. Such is the bustle that overtakes Tokyo Station, especially during rush hour. All the more reason to have an English language guide to tell you which JR line to hop on. I rely on the Hyperdia iPhone app to get around Tokyo, but I can imagine this machine would come in handy for tourists.
The Route Finder machine is inside the turnstiles, directly across from the Marunouchi central exit at ground level.