PROBLEM TO BE SOLVED : To establish a system for executing building construction and large reforming of a used building without fund by utilizing a lease for business of a short period in the article 24 of the Land Lease House Rental Act.SOLUTION : An active land fund combines the building, the lease for business of the article 24 of the Land Lease House Rental Act, a building buying method, a periodic lease of the article 38 of the Land Lease House Rental Act, and an active land type real estate security. An e-mail receiving part C1 receives e-mail M1 from a customer. A customer information data gathering part C2 gathers information on the customer from the content of the e-mail M1. A database control part C3 stores gathered data in a database. A data totalizing analyzing part C4 totalizes and analyzes the customer information. A customer information transmitting part C5 transmits the customer information from the data totalizing analyzing part C4 to a designated place.