A device for attaching a plug for heat-conducting tubes and thus block off the heat conducting tube, which is used to mount the plug for heat-conducting tubes to the heat-conducting tubes, the plug comprising: a plug main body which is formed so as to be capable of being inserted into the heat-conducting tubes, and is formed with a cylindrical closed end and a cylindrical open end; a columnar member which is capable of being inserted into and removed from the plug main body from the cylindrical open end of the plug main body, and in which an outer circumference is provided with a tapered surface having an outer diameter gradually decreasing in a direction of the open end of the plug main body when the columnar member is inserted into the plug main body; and a wedge member which is formed so as to be capable of being inserted into and removed from the plug main body from the cylindrical open end of the plug main body, and in which an inner circumference is provided with a tapered surface having an inner diameter gradually decreasing in the direction of the open end of the plug main body and opposing the tapered surface of the columnar member when the wedge member is inserted into the plug main body, said device comprising: a rod-shaped member in which a distal end inserted from the open end of the plug main body is fitted to the columnar member; a contact member into which the rod-shaped member is inserted, and in which a front end inserted from the open end of the plug main body comes into contact with an end of the wedge member; and a movement unit that moves the rod-shaped member such that the rod-shaped member is pulled out from the open end of the plug main body, said device being characterized in that the front end of the contact member comes into contact with the end of the wedge member, and a proximal end of the contact member comes into contact with a verge of opening of the plug main body in a state in which the tapered surfaces (22a, 23a) of the columnar member and the wedge member are opposed to each other. a plug main body which is formed so as to be capable of being inserted into the heat-conducting tubes, and is formed with a cylindrical closed end and a cylindrical open end; a columnar member which is capable of being inserted into and removed from the plug main body from the cylindrical open end of the plug main body, and in which an outer circumference is provided with a tapered surface having an outer diameter gradually decreasing in a direction of the open end of the plug main body when the columnar member is inserted into the plug main body; and a wedge member which is formed so as to be capable of being inserted into and removed from the plug main body from the cylindrical open end of the plug main body, and in which an inner circumference is provided with a tapered surface having an inner diameter gradually decreasing in the direction of the open end of the plug main body and opposing the tapered surface of the columnar member when the wedge member is inserted into the plug main body, a rod-shaped member in which a distal end inserted from the open end of the plug main body is fitted to the columnar member; a contact member into which the rod-shaped member is inserted, and in which a front end inserted from the open end of the plug main body comes into contact with an end of the wedge member; and a movement unit that moves the rod-shaped member such that the rod-shaped member is pulled out from the open end of the plug main body, said device being characterized in that the front end of the contact member comes into contact with the end of the wedge member, and a proximal end of the contact member comes into contact with a verge of opening of the plug main body in a state in which the tapered surfaces (22a, 23a) of the columnar member and the wedge member are opposed to each other.