Abstract: Disclosed is a threading device suitable for a building electrical pipeline. The threading device comprises a fan, a take-up and pay-off main machine and a connecting hose. A take-up state induction mechanism mainly composed of a bent pipe converging device, a first rotating shaft, a bent pipe converging device lifting spring and a first microswitch is creatively arranged in a ventilation bin. When a strong wire is tightened, the bent pipe converging device is easy to rotate along with tightening of the strong wire, and the strong wire makes contact with the first microswitch in time when being tightened. After the strong wire is loosened, the bent pipe converging device can automatically return under the action of the bent pipe converging device lifting spring, and the take-up state of a wire wheel is recovered.