PURPOSE: To continuously and surely form thin films on flat planar substrates by depositing the thin films on the substrates by evaporation after confirming the mounting of the substrates and a mask device for the substrates by a contactless type displacement meter at the time of depositing the thin films by evaporation on the substrates in a vacuum.

CONSTITUTION: Film formation is executed by carrying a cassette case 6 inserted with plural sheets of the substrates 5 into a vacuum forming chamber 1, driving a carrier 8 to take the substrates 5 mounted with the mask material out of the cassette case 6 and transporting the substrates to a film forming section. The contactless type displacement meter 12 is used and the distances between the displacement meter 12 and the substrates 5 as well as the mask 11 thereof are measured by control of a manipulator section 10 at this time. The measured values are sent to an arithmetic processing circuit 13 and a film forming device control section 14 where the values are compared with the preset numerical values. Judgment is made that the substrates 5 and the mask 11 are surely mounted if the measured values are within the set range. The film formation is then executed. As a result, the errors in the formation of the thin film on the substrates 5 by an error in the mounting of the mask on the substrates 5 is eliminated and the failure of the device and the degradation in the efficiency of the thin film production is prevented.