copper conductors of which respective wire diameter was 0 26 mm with the filler 207 at a pitch of 8 2 mm so that the conductor wires 209 were positioned at an outermost layer of the stranded conductors 211 then an insulation 213 comprising polyfluorocarbon rubber compound having the thickness of 0 4 mm was extruded and covered the stranded conductors 211 at 130 u00b0 c simultaneously with cross linking thereof by continuous cross linking method using pressurized steam at 200 u00b0 c and eventually the airtight cable 201 of which finished outer diameter was 1 7 mm was produced the airtight part was formed by using heat and pressure generated during cross linking of the insulation 213 through adhering power during hardening of the airtight material 205 comprising oil swellable polyfluorocarbon rubber compound whether or not compression was applied to the stranded conductors 211 and the swelling volume of the outer diameter of the filler 207 outer diameter increase rate were indicated in table 4 an airtight cable 301 according to this example is as per shown in fig9 and 10 an airtight material was extruded so that the outer diameter of the airtight material became 0 65 mm which served as a filler 305 as for the airtight material polyalkylene oxide resin aqua calk tw manufactured by sumitomo seika chemicals company limited serving as.