The invention discloses a boundary acoustic wave device (1). A quartz substrate (2) at least forms IDT (4) and an electric medium (3) is formed by the manner of covering IDT (4). The boundary acoustic wave is broadcasted at the boundary of the quartz substrate (2). The thickness of the IDT (4) is determined so that the velocity of the SH boundary acoustic wave falls below those of a slow transverse wave propagating across the quartz substrate (2) and a slow transverse wave propagating across the dielectric (3). The Eulerian angles of the quartz substrate (2) lie in the range with inclined line in Fig 13, thereby capable of using cheap quartz substrate, adopting SH boundary acoustic wave and improving the physics performance and characteristics of machine coupling coefficient K<2>.