1. An information delivery method for delivering prescribed contents to users registered in advance on a network, the network comprising: a first terminal; a presence server that manages presence information of a user of the first terminal; an information delivery server that stores contents to be delivered to the first terminal; a communication network that establishes connection among the first terminal, the presence server, and the information delivery server to enable communication, wherein the information delivery method comprises the steps of: forming a first presentity on the network sensed by the presence server, the presentity being an account necessary for the first terminal to enjoy presence service; providing the first presentity with a first identifier for uniquely identifying the presentity; forming an n-th presentity, which is an account necessary for the information delivery server to enjoy presence service; and providing the n-th presentity with an n-th identifier, wherein the information delivery server acquires presence information of the first user from the presence server through the n-th presentity, and when the acquired presence information matches delivery conditions of the stored contents, delivers the contents to the first user, with a delivery source of the contents as the n-th identifier.