PROBLEM TO BE SOLVED: To provide a rainwater drainage pipe structure capable of stably merging drainage from a branch pipe to a main pipe at a merging portion when draining rainwater by applying a siphon phenomenon. SOLUTION: The rainwater drainage pipe structure 100 includes a siphon type drainage member arranged on an upper floor and a main pipe 122 in which rainwater flowing from the siphon type drainage member flows down from the upper floor to the lower floor. , A branch pipe 150 connected to a merging portion 120T located in the middle of the main pipe 122 in the height direction and allowing drainage to flow into the merging portion 120T from the outside, and the main pipe 122 is on the upper side. It is characterized by including a first vertical pipe 123 arranged and a curing pipe 125 arranged below the first vertical pipe 123 and having a larger flow path area than the first vertical pipe 123. [Selection diagram] FIG. 4
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