A method for producing a single-crystalline film made of a single crystal of lithium potassium niobate-lithium potassium tantalate solid solution or a single crystal of lithium potassium niobate, comprising the steps of preparing a target made of a material for the single-crystalline film, preparing a foundation made of a single crystal of lithium potassium niobate-lithium potassium tantalate solid solution or a single crystal of lithium potassium niobate, irradiating upon the target, thereby gasifying molecules constituting the target by dissociation and evaporation thereof, and epitaxially growing the single-crystalline film on the foundation.