Thin film device and thin film inductor

Provided is a thin film device capable of ensuring operating performance by ensuring the adhesion of a conductive film and the magnetic characteristic of a magnetic film. A substrate has a surface roughness (an arithmetic mean roughness Ra) within the range expressed in the expression: X µm ‰¦ Ra ‰¦ 0.1 µm. A lower limit X of the surface roughness Ra is a value determined based on a series of parameters including an internal stress Ã, a thickness T, and an adhesiveness P per unit length of a conductive film. An anchor effect can be used to ensure the adhesion of the conductive film, and also ensure the magnetic characteristic (magnetic permeability) even when a magnetic film is provided on a substrate having a surface irregular structure.