PROBLEM TO BE SOLVED: To provide a repair method of a digestion tank made of a steel sheet capable of blocking easily a hole part on the digestion tank made of the steel sheet without stopping completely an anaerobic fermentation treatment, and suppressing second generation of a hole.SOLUTION: A hole 3a is blocked by pasting, for example, a water leakage repair tape 5 from the outside of a digestion tank 1 made of a steel sheet onto the hole 3a spot (for example, on a top plate 3) (first step). Thereafter, FRP lining 6 is applied onto the water leakage repair tape 5 from the outside of the tank (second step).SELECTED DRAWING: Figure 2