To easily prevent a ready mixed concrete placing hose from being dropped on the ground.

A docking hose 20 connected to a transferring steel pipe 11, and a tip hose 30 connected to the other end of the docking hose are connected to a boom by tying wires 14 whose one end is fixed to the boom 10 to fasteners 23, 33 fixed to sleeve fittings 22, 32 of respective hoses. That is, since the fasteners are already attached to a ready mixed concrete placing hose, it is unnecessary to prepare a drop preventing fitting, and the measures of drop prevention can be performed only by connecting the wires to the fasteners, and it is very convenient for a hose user. Since the wires extending from the boom are fastened to the fasteners, safety confirming work is easy, and detachment of the wires is also easy. Moreover, since the fasteners are lightweight in comparison with the conventional drop preventing fitting, handling is easy, and cost is low.