A piezoelectric thin-film acoustic wave device formed of a piezoelectric thin film of AlN on the +C plane and having the polarization strength of not lower than 0.63×10−20 F/V and an information processing unit using the same are disclosed. This is the result of the inventors having studied the factors other than the C-axis orientation affecting the electromechanical coupling factor and developing a method of improving the electromechanical coupling factor in view of the occasional fact that the electromechanical coupling factor cannot be improved by improving the C-axis orientation and the electromechanical coupling factor required for the piezoelectric thin-film acoustic wave device is not obtained. In such a case, the receiving sensitivity of the receiving system may be deteriorated and the transmission strength of the transmission system is required to be increased undesirably having an adverse effect on the power saving efforts.