To provide a cable surface printer keeping both of the density and viscosity of printing ink constant.

The cable surface printer 10 prints a character, a figure, or a mark on the surface of a cable 12 by using the printing ink 11 obtained by blending ink with a solvent. The cable surface printer 10 includes: a thermometer 18 measuring the temperature of the printing ink 11; a temperature adjustment means 19 adjusting the temperature of the printing ink 11 based on the measurement value of the thermometer 18; a viscometer 20 measuring the viscosity of the printing ink 11; and a viscosity adjustment means 21 adjusting the viscosity of the printing ink 11 based on the measurement value of the viscometer 20. The viscosity of the printing ink 11 is kept constant by the viscosity adjustment means 21 while the temperature of the printing ink 11 is kept constant by the temperature adjustment means 19, so that the density of the printing ink 11 is kept constant.