PURPOSE: To prevent the leakage of ink from a slit due to the expansion of air in an ink tank by mounting a heat-insulating section between a head proper and the ink tank.

CONSTITUTION: A printing head 10 consists of a head proper 11 and an ink cassette 12, and an ink tank 20 in which ink 19 is stored is formed to the ink cassette 12. The ink cassette 12 is mounted to the upper section of a guide section 15, and the tips of needles 13 are arranged in slits 23. A heat-insulating section 27 is disposed to the upper surface of the guide section 15, and brought into contact with the lower surface of the ink cassette 12. Heat generated from a driving section 14 is transmitted over the guide section 15 on printing, and the temperature of the guide section 15 is elevated to a high temperature during continuous operation, but heat is not transmitted over the ink tank 20 by the heat-insulating section 27, and air on the inside does not expand. Accordingly, the slits 23 are supplied with a fixed quantity of ink 19 corresponding to the quantity of reduction at all times, thus generating no ink leakage from the slits 23, then keeping the stable state of printing.