A change machine
is a device that accepts large denominations of currency
and returns an equal amount of currency in smaller bills
. Typically these devices are used to provide coins in exchange for paper currency.
In the US, these devices are typically seen in the vicinity of devices that will not accept paper currency. This can be in a parking facility that has parking meters, or, in the past, near vending machines.
Before the advent of coinless slot machines, casinos would sometimes have change machines that would accept paper currency and return coins or tokens that could be used in the machines.