PROBLEM TO BE SOLVED: To provide a method capable of easily arranging a drainage separator on a floor surface by folding a belt-shaped sheet that is prevented from deformation or damage during storage or transportation, and provide a belt-shaped sheet used for the method.SOLUTION: A drainage separator Pcomprising a standing part 10 and a floor surface sticking part 20 is formed by folding an approximately flat belt-shaped sheet Scomprising: standing part formation planning regions 1 extending in longitudinal direction; a floor surface sticking part formation planning regions 2 arranged on one or both sides of the standing part formation planning regions 1 in an extending manner thereto, and straight folding planning regions 3a, 3b which are formed between the planning regions or between the planning regions and standing part formation planning regions and extending in longitudinal direction. The floor surface sticking part 20 is stuck on floor surface F. The approximately flat belt-shaped sheet Sis free from
