To actualize on a network a negotiation place where a user who requires a communication band can speedily rent the communication band meeting requested conditions, from a carrier.

The user who uses a communication band posts conditions of desired guaranteed width of the communication band to the ground to be rented, communication quality, reliability, etc., together with the desired rental price, the carrier selects a user's request which meets or nearly meets the conditions among communication bands that the carrier can provide and posts the rental price, etc., to an application bulletin board on a WWW server, and the user selects one of applying carries and makes a rental contract. As a method for making the contract, what is called an auction system, where the contents on the WWW server that carriers apply can be viewed by other carriers and negotiations can also be made and the so-called 'bidding system' which disables application contents of other carriers to be viewed can be adopted.