To smoothly force-feed sediment, particularly the sediment having a somewhat high moisture content, hardly cause blocking in the middle of a transportation pipe, and relatively facilitate the formation of a plug.

The sediment fed into the transportation pipe 8 is force-fed by compressed air together with the bubbles generated by blowing air into an aqueous solution including a surfactant. The bubbles form a smooth surface on the inner wall of the transportation pipe 8 and contribute to the reasonable force feed of sediment by a bearing action. This force feed device is basically provided with the transportation pipe 8, a sediment feeding means 1 to the transportation pipe 8, a blower 4 feeding the compressed air to the transportation pipe 8, a foaming device 5, and a bubble feeding means to the transportation pipe 8. A plurality of switch valves 13a, 13b, etc., are arranged at intervals in the longitudinal direction on the transportation pipe 8. The switch valves 13a, 13b, etc., are opened in sequence at time differences by a control means 16, and the compressed air is fed when they are opened.