To provide a sand removing device in a dam capable of suppressing costs of investment in facilities to a comparatively small extent, being installed even in an existing dam without any difficulty and trouble, and preventing organic polluted sludge affecting the environment on the downstream side adversely and causing its pollution from being discharged.

This sand removing device in dam is constituted in such a way that a pipe for removing sediment and draining water is installed from the upstream side to the downstream side of the dam across the dam, a suction port of the pipe on the upstream side is provided on a ford apart from the dam to move around in order to suck sediment and water through the suction port based on the principle of a siphon, and the pipe on the downstream side of the dam is installed to let them flow down from a high position of the dam to its lower end so that pressure of the water in the pipe on the downstream side acts on the suction port due to head in the dam.