To provide a water gate installation method capable of securing with ease watertightness of a water gate and a water channel structure, and reducing the construction term when securing the water gate to the water channel structure.

A molding material as a substitute for an ordinary wooden molding has a structure integrated with the water gate in a manufacturing factory shop at the peripheral four sides of the water gate when manufacturing the water gate, thereby, execution accuracy at construction site is enhanced and process of construction work can be reduced, hence, the watertightness of the water gate and water channel structure can be secured with ease and further, the construction term can be shortened. Accordingly, the term of the construction work and restriction of the term can be removed and improvement of the total cost can be realized.