A piezoelectric actuator with a reinforced bending mode to suppress bending resonance caused by extension/contraction movements of the piezoelectric actuator and a disk drive using the piezoelectric actuator are provided. A flexible substrate is separated by a slit. A first piezoelectric element unit and a second piezoelectric element unit, both showing extension/contraction displacement, are disposed on one of the slit-separated flexible substrates, respectively. A coupling portion is provided to couple the separated flexible substrates across the slit. The coupling portion is provided at a position corresponding to an antinode of a primary bending mode of the first and second piezoelectric element units being respectively fixed in both ends.