Pachinko is a device used for gambling and is a mixture between a pinball machine and a video poker machine. Pachinko parlours are widespread throughout Japan.
The way the machine works is you buy buckets of ball bearings and insert them into the machine in a bid to acquire more balls, then you can exchange the balls for prizes. As slot machine gambling is illegal in Japan you cannot play for cash, but nearly all Pachinko Parlours also have an exchange window so you can exchange your prize for cash. Thereby getting around the anti gambling laws.
The machines originally were all mechanical and operated much like a vertical pinball machine, but today they include flash displays that involve a slot machine type function giving some of the parlours the name Pachi-slot.
While the adventure of using and playing Pachinko is probably left to the locals, or someone that has a solid grasp on the Japanese language, we highly recommend taking a quick walk through a Pachinko Parlour to experience the sound of disco music playing so loud to try and drown out the sound of thousands of metal balls being pumped into the machines at any one moment. There are thousands of flashing lights in these places along with a constant cloud of tobacco smoke.