To provide a purchase and sales support system for a house with which the house is purchased on the initiative of a purchaser of the house and information collection cost and a operating cost of a seller of the house are also reduced.

In the purchase and sales support system of the house constituted of a terminal 1 of the purchaser or the house, a terminal of the seller of the house and an information managing device 3 of a service provider for providing service and constituted by connecting the terminal 1 of the purchaser of the house with the information-managing device 3 of the service provider via a communication network 4 and connecting the terminal 2 of the seller of the house with the information-managing device 3 of the service provider via the communication network 4, it is characterized by providing a means by which purchase negotiation of the house is repeatedly performed on the initiative of the purchaser of the house, by interposing the information managing device 3 of the service provider between the terminal 1 of the purchaser of the house and the terminal 2 of the seller of the house, and performing relaying service of information about the purchase of the house and a suggestion by the seller of the house by the information-managing device 3 of the service provider.