An available bandwidth estimating device 300 is equipped with: a transmission rate acquiring part 301 configured to acquire a transmission rate, which is the amount of data transmitted by a transmitting device per unit time to a receiving device connected so as to be capable of communicating via a communication network; and an available bandwidth estimating part 302 configured to estimate the available bandwidth based on a mathematical model constructed by representing a relation between an available bandwidth, which is a communication bandwidth available in a communication path between the transmitting device and the receiving device, and the transmission rate by a dynamic model including a mobile body movable in a preset moving direction and an elastic body transforming in the moving direction by a movement amount of the mobile body having moved in the moving direction, and based on the acquired transmission rate.