To solve a problem that a drop preventing net installed at the lower end of a manhole steel lid is floated and scattered together with the manhole steel lid, thus causing a drop accident when the rainwater of the planned downflow capability or above flows into a conduit at a heavy rain and the rainwater floods from a manhole in the sewerage conduit installed under the ground.

A drop/flotation preventing net stopper lock pawl 5 and a drop/ flotation preventing net stopper pawl 6 are fitted to the tip of the drop/flotation preventing net 3 to prevent the drop-flotation preventing net 3 from being floated and scattered even if the manhole steel lid 10 is floated and scattered, therefore the drop/flotation preventing net 3 is not floated, thus securing safety. A pulley 7 for carrying-out the slurry in the conduit is fitted to the drop/ flotation preventing net 3, and it can be used as the pulley 7 for emergency evacuation by fitting an emergency rope to it at an emergency. Grade adjusting and height adjusting bolt holes 13 are fitted to a receiving frame connecting ring 9, therefore a manhole receiving frame 1 can be simply installed according to the road grade.