PURPOSE: To form a magnetic thin film with stable quality on a film by connecting a ferromagnetic material evaporating source part with a travelling part of the film through a slit having size regulated by the oblique evaporated surface and the evaporating surface of the evaporating source part.

CONSTITUTION: If electron beams 11 are irradiated on the surface of an evaporating material when the film 1 on which a magnetic thin film is to be formed travels along a rotary supporting body 3, the irradiated evaporating material is gasified and the gas flow is reached and adhered to the evaporated surface 9 of the film 1 through the slit 10. Since the slit 10 is formed with the length regulated by the length L of the evaporating surface of the ferromagnetic material and the evaporated surface 9 of the film 1 and the width regulated by the width of the film 1, the adhering reaction area of oxidative gas is restricted almost by the evaporated surface 9 of the film 1 and the quality of the magnetic thin film formed on the film 1 is stable within a comparatively short period.