PURPOSE: To easily and quickly design a building reflecting the intension of a client by recognizing parts where walls for supporting the building among the walls surrounding rooms based on the arrangement of the rooms decided by the client can be arranged as wall lines and confirming whether or not the amount of the walls which can be arranged on the wall lines can maintain the actual strength of the building.

CONSTITUTION: When the client decides the arrangement of the rooms of the building based on his/her own demands, the positions of the walls surrounding the respective rooms are inputted by a design input means (a)). A wall line preparation means (b) prepares the wall lines for indicating the walls for supporting the building among the inputted walls surrounding the respective rooms and a wall amount checking means (c) judges whether or not the amount of the walls which can be arranged on the prepared wall lines is sufficient for supporting the building. Then, a structure model preparation means (d) allocates panels to the areas of the walls, a floor and a roof based on the wall lines prepared by the wall line preparation means (b) and decides the structure of the building. Thus, the building reflecting the intension of the client is easily and quickly designed.