A web-based mobility guaranteeing method includes, at a terminal, connecting to a first service providing apparatus; transmitting a service request signal for requesting service information to the first service providing apparatus; at the first service providing apparatus, transmitting a service providability inquiry signal to a web-based service providing apparatus, based on whether or not the service information is able to be provided by the first service providing apparatus; at the web-based service providing apparatus, transmitting the service providability inquiry signal to a second service providing apparatus, receiving a service providability response signal from the second service providing apparatus, and changing a service provider of the terminal from the first service providing apparatus to the second service providing apparatus; and at the terminal, receiving a service response signal from the second service providing apparatus in response to the service request signal.