To provide an injection method wherein hardener slurry, which can achieve improved hardening characteristics and durability for the ground having high natural water content or the ground containing organic acids, without producing bleeding, is injected, and in which there is no need to treat sludge liquid.

Hardener slurry 8 containing colloidal silica and cement solidification agent, as components, is sprayed against the ground by means of a high pressure jet stream to form a solidified body 7. The slurry 8 is prepared by a method wherein a first mixed liquid is prepared by mixing colloidal silica and water at a weight ratio of 1:3-8 and a second mixed liquid is prepared by mixing cement solidification agent and water at a weight ratio of 1:1-4 and the first mixed liquid and second mixed liquid are mixed by either a 1, 5 shot or 2 shot method.