To provide a support column installation structure replacing wooden support columns used in a simple structure such as a signboard, a protective fence or the like with new ones even if the wooden support columns become deteriorated with age.

This support column installation structure is constituted by forming a middle hole 12 for inserting the support column 21 in a foundation block 11 and forming an expanding slot 22 for dividing a cross section into a plurality of sections at a lower part of the support column 21 by using the wooden support column 21 and the foundation block 11 buried into the ground to hold the support column 21. A lower face and a side peripheral face of the support column 21 are covered with a sheet 18 to block the expanding slot 22, and a clearance between the middle hole 12 and the support column 21 is filled with a filler 16 to install the support column 21. Since the expanding slot 22 is provided, the support column 21 buried into the foundation block 11 can be easily separated from the filler 16 and can be simply pulled out. Only the support column 21 can be replaced with a new one in a short time by removing the filler 16, too.