To provide an installation structure of a foundation block for a guardrail, which allows easy installation stably and easily and surely supports the guardrail and easily provides planting between the foundation block and the guardrail.

The foundation block 1 can be easily installed in the stable state with a low wall 3 thereof, and the guardrail 2 and a post 2a supporting the guardrail 2 can be easily supported by a post supporting hole 4 of a rising wall 5. Planting 8 can be easily and surely provided in planting space parts 6 formed securing a sufficient space by forming the rising wall 5 to rise high. The respective planting spaces 6 are opened at the upper parts on the guardrail 2 side on both sides of the post supporting hole 4, and formed so that two space shapes and positions are symmetrical. The planting 8 can thereby be easily and surely arranged in fine appearance in the clearances between the rising wall 5 and the guardrail 2.