To bring the inside of a siphon pipe into a full water state efficiently when starting a siphon by eliminating the need to provide a check valve in a water source side conduit of the siphon pipe.

A siphon intake system 10 comprises a siphon pipe 12 which is laid over a dam body 100. A degassing part 40 which sucks air in the siphon pipe 12 is connected to a pipe top of a dam body top conduit 12b of the siphon pipe 12. Furthermore, the siphon intake system 10 comprises a water injection part 48 for preferentially injecting priming water to a water supply side conduit 12c. When starting a siphon, priming water is injected preferentially from the water injection part 48 to the water supply side conduit 12c by using a water injection pump 60. After the water supply side conduit 12c is brought into a full water state, the degassing part 40 is used to suck the priming water into the water source side conduit 12a, and the entire siphon pipe 12 is brought into the full water state.