PURPOSE: To make the increase of dot density, the speed up of printing speed and the miniaturization of head possible by controlling the rise of the cooling temperature of heating part, by a method wherein a space is provided in a substrate and only a gas is enclosed therein as heating medium.

CONSTITUTION: A substrate 1 has a space therein and only a gas is enclosed in this space as heating medium. For example, the substrate 1 is made of aluminum sheet 1a of 2mm in thickness presenting the boxy state of 10mm in height in which a space is formed and helium gas 1b of 1atm. is enclosed in this space. Thereby, the heat generated at a heating part 2 is absorbed into the helium gas 1b enclosed in the space of substrate 1 via the aluminum sheet 1a of high heat conductivity and the heat absorbed in the helium gas 1b is emitted from the bottom surface 1c of aluminum sheet 1a. At the same time, because helium gas 1b has a good heat conductivity, the temperature of helium becomes uniform in abovementioned space, the temperature rise with the passage of time of heating part 2 is restricted and at the same time, the temperature distribution of heating part 2 is equalized.