After arriving at the Arashiyama station, the 「駅之足汤」 can be seen from the direction of the train moving forward, but the ticket office is in a small house on the right side of the station entrance (The red circle on the picture). Also you could rent a bike at this ticket office.
Since the train charges when get off, I didn’t buy tickets at「こうりゅうじ」station, then I paid some cash at the platform entrance.
But I had no idea that I should exit by paying first, or buy ticket to have a food bath first.
When I was looking around the ticket station, one kind-hearted old man came and asked if I wanted to rent a bike. With my poor Japanese, I explained that I would like to buy a ticket for foot bath, thus the old man showed me the way and helped to call the service people. What nice Kyoto people!
Well, the train ticket can be paid after the foot bath then.