To provide a device for drilling under continuous flow, which is suitable for inserting a stop valve for stopping the flow of a fluid in an existing pipe and removing the inserted stop valve.

This device for drilling under continuous flow includes a sealed case 9 having divided cases 21, 22 surrounding part of the existing pipe 1 and a valve cover part 92 joined to a branch pipe part 27 projecting upward of the existing pipe 1, a stop valve element 90 which is enclosed by the valve cover part 92 and the branch pipe part 27 and intruded into the existing pipe 1 to stop the flow of the fluid in the existing pipe 1, a working valve element 5 in an arcuate shape in cross section which opens and closes a branch hole 28 formed in the branch pipe part 27 by rotating in the circumferential direction of the existing pipe 1, and a rotating mechanism 6 for rotating the working valve element 5. The rotating mechanism 6 includes an operation part 67, a rotating drive gear device 63, and a driven gear 51 for rotating the valve element 5 for working in the circumferential direction of the existing pipe 1 by the rotation of a drive gear device 63.