PURPOSE: To stably keep the level of the cooling medium in a cooling pipe and to prevent the evaporation of the cooling medium in the vicinity of the surface thereof by a method wherein the cooling medium is supplied to the cooling pipe cooling a rubber coated cable after vulcanization to be allowed to always overflow from a predetermined cooling medium level position to be stored in a level detection pot and discharged from the pot at a constant speed to hold a definite amount of the cooling medium in the pot.

CONSTITUTION: A vulcanizing pipe 4 and a cooling pipe 5 are directly connected and a cable core 1 is drawn into the vulcanizing pipe 4 through a spline box 8 and drawn out through a cooling pipe 5 and a water seal 8. An escape pipe 25 is provided to the part of the surface 7a of the cooling water 7 of the cooling pipe 5 to allow the cooling water 7 to overflow. A level detection pot 26 is connected to the pipe 25 and the cooling water is discharged from the escape valve 27 provided to the lower part of the pot 26 by a definite amount. In a supply water control part 30, the liquid level position in the pot 26 is detected by a differential pressure detector 31 and compared with a referece position to output a predetermined signal. A level controller 32 controls a water supply control valve 33 on the basis of the signal to increase and decrease the amount of the water supplied to the cooling pipe 5.