Communication system, portable terminal, movement management device, and communication control method

Provided is a communication system comprising: a portable terminal; a movement management device which performs movement management for the portable terminal; a first gateway which connects the portable terminal to a first network; and a second gateway which connects the portable terminal to a second network. On the basis of the result of a determination as to whether the portable terminal is to be connected to the first network via the first gateway or the portable terminal is to be connected to the second network via the second gateway, the movement management device switches between causing the portable terminal to use first contract information for connecting to the first network via the first gateway, or to use second contract information for connecting to the second network via the second gateway.