An ink jet printer head of hot-melt type for heating and melting solid ink and then discharging the melted ink onto a recording medium is provided with: a cavity plate prescribing (i) an ink flow path through which the melted ink is supplied, (ii) a plurality of ink storing chambers, each of which is connected to the ink flow path in which the supplied ink is temporarily stored, and (iii) a plurality of ink discharge holes which are connected to respective one of the ink storing chambers though which the temporarily stored ink is discharged; a piezoelectric element member, which is opposed to the cavity plate and has a plurality of piezoelectric elements for selectively changing capacities of the ink storing chambers; and a base member for supporting the piezoelectric element member. The piezoelectric element member is interposed and fixed between the cavity plate and the base member. The cavity plate, the piezoelectric element member and the base member have thermal expansion coefficients equal or approximate to each other.