The present invention relates to a method for changing service quality of a content adaptively. In the present method, when allowance of access to a network is requested, whether transfer speed demanded by the request of access allowance can be provided is checked. If can not be provided, service quality of a connection being serviced is lowered. In the meantime, the present method monitors whether available bandwidth is generated, and upgrades service quality of a connection being serviced when available bandwidth is generated. The above operations can make a given network resource fully used.