To facilitate manufacturing a composite substrate which is used for an acoustic wave element and has a relatively simple structure while variation in size with temperature is smaller than that of a substrate formed only by laminating a piezoelectric substrate with a support substrate together.

A method includes preparing a silicon substrate 12, an LT substrate 10 capable of propagating SAW, and a resin film 18 in the same shape with the LT substrate 10. Then the LT substrate 10 is coated with an organic adhesive 13 and stuck on the silicon substrate 12, and the resin film 18 is put over the silicon substrate 12 and then heated to form a stuck substrate 16. Further, the top surface of the LT substrate 10 is polished by a polishing surface plate to polish the top surface into a mirror plane while reducing the thickness of the LT substrate 10.

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