In urban areas in Japan, the method of entering and exiting railroad stations by touching a prepaid IC (Integrated Circuit) card on a ticket gate is widely practiced. For this reason, some station ticket gates are equipped to handle IC cards only. These machines do not have a paper ticket slot, and in many cases are marked with a large IC sign so that they can be seen from outside the ticket gate.
At large stations in urban areas, many people stream through the ticket gates one after another, touching their cards to the machines. If you are trying to board a train with a paper ticket and accidentally get in line for an IC card-only machine, you will not be able to pass through the ticket gate and cause some confusion. If this happens, please move out of the line and wait until the flow of people has subsided before looking for a ticket gate that you can use. IC cards for tourists visiting Japan are also available, so you may want to use them.