To provide a civil engineering excavation device enabling a boring bit installation operation and a drilling rod joining operation to be efficiently and safely performed.

A hole allowing a boring bit to extend therethrough is opened in the rotating part of a rotary table. A sliding cap detachably fitted to the rotary table is attached to the hole to close the hole. The rotational torque of the rotary table is transmitted to a drilling rod through the sliding cap to rotate the boring bit connected to the end of the drilling rod for excavation. A block part is provided to the sliding cap, and inserted under a block receiver provided to the drilling rod side during the drilling rod joining operation to fix the drilling rod to the rotary table.