To provide a sluice gate suitable for a water non-cutoff installation method, and the water non-cutoff installation method of the sluice gate in which a space of a gate room is not required as a flow passage after the sluice gate is installed.

When installing a sluice gate 1 in a flow passage pipe 13 penetrating a gate room R, the water non-cutoff installation method implements the steps of, in order: (1) cutting the flow passage pipe 13 within the gate room R; (2) mounting a communicating pipe 21 formed from double pipes to the sluice gate 1 beforehand and carrying the sluice gate 1 into the gate room R while contracting the communicating pipe 21; and (3) elongating the communicating pipe 21, fixing the sluice gate 1 to a skeleton 12 of the gate room R while communicating an end portion of the communicating pipe 21 to one cut end of the flow passage pipe 13, and fixing a door stop installation body 28 to the skeleton 12 around the other cut end of the flow passage pipe 13.