Abstract: An ATM operation supporting system for managing the number of bills in a plurality of ATMs. The system includes a mobile cart, a counting section, and a control section. The mobile cart has a handling mechanism capable of installing a bill cassette into each ATM and removing the bill cassette from each ATM. The mobile travels to each ATM and installs and removes the bill cassette using the handling mechanism, thereby performing bill replenishment/collection operation for each ATM. The counting section counts the number of bills stored in the bill cassette which is directly or indirectly loaded onto the mobile cart by a clerk in charge. The control section controls the bill replenishment/collection operation performed by the mobile cart such that the numbers of bills in the ATMs are balanced. The ATM operation supporting system can manage the number of bills in an ATM, thereby realizing efficient utilization of cash as well as easing the operational burden on a clerk in charge.