To automatically and repeatedly perform estimation calculation by generating a picture on which it is possible to easily compare data prior and posterior to a renovation construction.

This renovation cost calculation system is provided with a plotting control means 20 for adding a display code 29 to designate symbol image data 28 of established construction and plotting information to CAD data 50 for reformation construction when the CAD data 50 for renovation construction are generated by using CAD data 48 prior to renovation; a difference extraction means 22 for extracting a difference between the CAD data 48 prior to renovation and the CAD data 50 for renovation construction; a member quantity extraction means 23 for extracting member quality 45 of a member included in the construction; and a renovation construction cost estimation means 24 for outputting a construction cost estimate 46, wherein a floor plan picture on which symbol image data 28 of the established construction and removed construction are displayed so as to be classified by color is redisplayed on a display 14 in a compilable state.

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