PURPOSE: To conduct a cooling with high efficiency and simple construction by providing a cooling liquid flow path for cooling a heating element within a head substrate, an expanded-diametered part in a part of the liquid flow path, and a heat release member in the vicinity of the expanded-diametered part.

CONSTITUTION: The rate of flow of a cooling liquid which flows through a flow path from a cooling liquid inlet 6 to a cooling liquid outlet 4 is lowered at an extended-diameter part 3 according to the cross-section area thereof. Therefore, a sufficient heat release time by a heat release fin 5 is ensured. Additionally, if the extended-diameter part 3 of the flow path has the cross-sectional area and length suitable for an ink reservoir, it can also serve as an ink reservoir. If a quantity of heat generated in a heating part is too large, it is preferable that a forcible cooling is conducted by blowing air to the fin 5 by a fan. In this manner, the heating element can be efficiently cooled with a simple construction.