Acoustic touch sensor

A coordinate input device of touch-type capable of giving an electric signal to a transducer, even if said transducer is disposed on a back surface of a substrate. The device contains acoustic wave transducers (piezoelectric vibrators), each functioning for oscillating a bulk wave (a first wave) toward a top surface of a substrate; a planar wiring formed on a back surface of the substrate by, e.g., transfer printing with conductive paste, for supplying the piezoelectric vibrator with electric power; diffractive acoustic wave mode couplers, each functioning for converting said bulk wave into a surface acoustic wave (a second wave) and vice versa; and a detector to detect scatter in the surface acoustic wave on the top surface of the substrate. Employing the planar wiring allows the wiring to be disposed even on the back surface of the substrate and also it may resolve the problem of fragility associated with a cable wiring.