An apparatus for and a method of non-destructively determining properties of a SAW substrate, in which first and second interdigital transducers are formed in a spaced relationship on a single common piezoelectric substrate, a blocking member is formed between said transducers on the substrate for preventing an acoustic wave signal from being transferred between said transducers via the common substrate, spacers are provided for supporting a to-be-determined SAW substrate above the common substrate with a spacing left between the SAW substrate and the fingers of transducers, the SAW substrate to be placed on the spacers is positioned with respect to the transducers so that co-directional mode coupling will, in operation, effectively take place between the SAW substrate and the transducers, adherence between the SAW substrate and the spacers is secured to enhance the co-directional mode coupling, an electric signal is applied to the first transducer for transferring, due to the co-directional mode coupling, an acoustic signal to the SAW substrate along the surface of which the acoustic signal will propagate and will be transferred, due to the co-directional mode coupling, to the second transducer, and the output of the second transducer is measured.