PURPOSE: To form a vapor deposited film having extremely high purity on a substrate with good efficiency of the vapor deposition by separating and removing the gaseous raw materials incorporated into the gas ionized by a mass separator provided in the ion beam vapor deposition device.

CONSTITUTION: The gaseous raw materials are introduced from an introducing port 1 into an ionizing chamber 2 and are ionized by a plasma discharge, etc. The ions are accelerated by an acceleration electrode 4 in an acceleration electrode chamber 3 and are passed as an ion beam 5 into an acceleration tube 6 to adjust and accelerate the magnetic field of the mass separator 20 constituted of the curved acceleration tube 6 and an electromagnet 8. The gas ions form the specific orbit determined by the charge and mass and only the ions having the same orbit as the curvature of the acceleration tube 6 among these ions enter a sample chamber 13 in a high-purity state. The thin film by the ions is thus deposited by evaporation on the substrate 12. First and second cooling cylinders 15, 16 using liquid N and liquid He are disposed in the acceleration tube 6 in such a case to cool, condense and remove the non-ionized gaseous raw materials. Only the ionized gas of high purity is introduced into the sample chamber 13. The vapor deposited film having the extremely high grade is thus formed on the substrate 12.