A thin film piezoelectric element according to the present invention includes a potassium sodium niobate thin film having a structure in which a plurality of crystal grains are present in a film thickness direction; and a pair of electrode films sandwiching the potassium sodium niobate thin film. When the potassium sodium niobate thin film is divided into three regions of the same thickness in the film thickness direction and average crystal grain sizes A1, A2, and A3 of the respective regions are determined, a ratio m/M of the smallest average crystal grain size m among A1, A2, and A3 to the largest average crystal grain size M among A1, A2, and A3 is 10% to 80%. The region having the smallest average crystal grain size m lies next to one of the pair of electrode films.