To provide a blocking device capable of simply and inexpensively coping with increase of branch pipes without deteriorating fire resistive property.

The blocking device 1 is composed of a short pipe 3 of synthetic resin having an end 8 fitted and adhered to a branch pipe connection opening 9 which is provided in a joint inner pipe 2a of a fire resistive dual collecting pipe joint 2, a cap 5 of synthetic resin adhered to the other end of the short pipe and coated with fiber mixed mortar, a mortar pipe 6 loosely fitted onto an outer periphery of the short pipe with a fitted-in portion 10 left for the branch pipe connection opening, and a fire resistive tape-like joint 7 wound on an outer peripheral surface of a connection part between a cap and the mortar pipe. A gap 11, in which a cutting tool 13 for cutting the short pipe can enter, is provided in the connection part, the length of the mortar pipe is set to be a length suited for fitting of a piping socket 20 and the outer diameter of the mortar pipe is set to be larger than the outer diameter of the joint inner pipe.