To prepare a large amount of self-fluiding hydraulic composition having very fast hardening property in a short time by transporting it to a jobsite in a form of powder, and kneading it with water by a continuous kneading method to prepare slurry so as to be flowed in at the jobsite.

A continuous kneading method uses a kneading mixer provided with a powder-supply feeder and a device for supplying quantity of water with a water meter capable of the continuous supply of self-fluiding hydraulic composition powder. The ratio of water to powder can be substantially constantly kneaded by controlling the powder-supply feeder and the water meter mounted on a kneader, and slurry having a constant flow value is continuously supplied. The flow value of slurry is preferably 190-250 mm. A large amount of self- leveling material slurry whose secular change of the fluidity is large can be prepared at a jobsite.