PURPOSE: To obtain a roadbed having sufficient strength while combining with the recycling of waste material by crushing the waste material such as concrete or asphalt into a given or less grading to be a granular body, and adding a coagulant to a mixture of the granular body at a given ratio.

CONSTITUTION: A roadbed is formed by crushing waste material such as concrete and asphalt into a granular body having an dout 10mm or less size, and solidifying the mixture of the granular body with portland cement. Though the uniaxial compression strength or the breaking deformation of the roadbed varies by the adding quantity of the portland cement, the adding ratio of the portland cement is made about 4% or more for obtaining a roadbed having an uniaxial compression strength of about 10kgf/cm2 or more. This can eliminate the need for the direct cost for roadbed material, and conduct low-cost roadbed construction.