The invention provides an ink jet head which exhibits a good response characteristic through heating and fast cooling enough to implement high-speed printing. A nozzle plate (10) having a nozzle orifice (11), and a substrate (7) constitute part of a peripheral wall of an ink chamber (31). A pressure generating member (20) is provided in the ink chamber (31). The pressure generating member (20) has a buckling member (1), a heater layer (3), and a diaphragm (5). The buckling member (1) is formed into a generally plate shape and its peripheral portion is attached to the substrate (7). The buckling member (1) can be switched between a no-displacement state in which it undergoes substantially no thermal stress, and a buckled state in which it is thermally expanded and buckled. The heater layer (3) is provided along a surface of the buckling member (1) on the substrate (7) side. The diaphragm (5) is composed of a generally plate-shaped flexible material and provided along a surface of the buckling member (1) on the nozzle plate (10) side in such a state that at least its peripheral portion (5c) is attached to a peripheral portion (1c) of the buckling member (1).