To smooth the push in of a linear body into a conduit line, by setting the length of a top guide rod with a specified outside diameter to be larger than the specified maximum length and smaller than the specified dimension, when it is made with the specified maximum length where a virtual column rigid body with a specified outside diameter can be inserted along the trough of a cable strand into the vacant space of a conduit line.

It is assumed that a triplex type of CV cable 6 comes to the opposite poles of the lowermost position and the uppermost position within a conduit line 7, at the first position a and the second position c at mutual interval of p/3, with the strand pitch of the triplex type of CVD cable 6 being p. Then, when it is defined that the maximum length where the virtual column rigid body 10 with a specified diameter d can be inserted along the trough 12 of the cable strand into the vacant space of the conduit line 7 is L0, the length L of the tip guide rod with a specified outside diameter d is set to be larger than the maximum length L0, and besides to be smaller than (L0+100 mm). As a result, a linear body can be pushed in smoothly and besides surely into an existing conduit line 7.