The present invention provides a method for producing a synthetic diamond thin film (2) which comprises decomposing with microwave a raw material gas containing at least one compound selected from the group consisting of carbon monoxide, carbon dioxide and a hydrocarbon and hydrogen or hydrogen and oxygen to produce a plasma and contacting the plasma with the surface of a substrate (1) held outside the area irradiated with the microwave to form a diamond thin film (2) on the substrate (1). The present invention further provides an apparatus for producing a synthetic diamond thin film and a synthetic diamond thin film and devices in which the synthetic diamond thin film is used.