To provide a device for perforating a center hole as a primary communication hole in a main pipe lining material closing a branch portion of a branch pipe, where the branch pipe is mounted, having compact construction and improved durability.

The device comprises an air motor 11 fixed to the front end of an operation rod and having a rotary perforating cutter 12 mounted at the front end and a lock hole 17 in the rear end, a motor supporting sleeve 21 for supporting the air motor 11 to be axially replaceable as predetermined, an air inflated branch pipe pressing cylinder 31 forming an air chamber 34 between the motor supporting sleeve 21 and itself, and an air unlock type motor locking means 36 mounted at the rear end of the motor supporting sleeve 21 and having an air duct 41 communicating with the air chamber 34 and a lock pin rod 39 lock-engageable with the lock hole 17 of the air motor 11.