You have one of the many variations of the Groetchen Pok-O-Reel trade stimulators from about 1933. They were found in 3 or 5 reel variations with and without gum vender.
They are nice collectible machines; yours has been spray bombed, is missing the top marque and I think the reel strips have been replaced.
I don't know what the little window and knob on the right front is for or what it does, but I doubt very much it is original to the machine. I assume you use the knob to select your horse number in the little window; if you can change it after the reels have stopped, you know it's bogus.