To provide a surface acoustic wave element baseboard which is formed by directly adhering a piezoelectric body thin film which is superior in properties regarding crystallinity, an electromechanical coupling coefficient and propagation loss, without deteriorating property concerning the propagation speed of a high sound velocity baseboard, etc., to the high sound velocity baseboard, such as diamond.

The front surface of the high sound velocity baseboard is worked to a mirrored-surface finish, the piezoelectric body thin film is formed on a support baseboard, constituted of a material which does not give damages to the piezoelectric body thin film when it is removed. The high sound velocity baseboard and the piezoelectric body thin film are subjected to hydrophilic treatment impartation and integrated through heating. Then the support baseboard is removed by a method, such as acid treating, to obtain an optimum surface acoustic wave element baseboard which is used in high-frequency band.