PURPOSE: To make it possible to monitor and to measure the thickness of coating easily and correctly, by installing a making means between a rotatable holder provided with plural sample- attaching holes in circumferential direction and an evaporation source for coating material, the masking means shielding the portions excepting the sample-attaching holes.

CONSTITUTION: A substrate 16 made of, e.g., glass etc. is placed on each of sample-attaching holes 83... made in a rotatable holder 8, then a motor 13 is operated so as to position a predetermined hole 83 on a mask hole 15. Monochromic light is irradiated on the substrate 16 placed on the hole 15 through a window 17 of a bell jar 3, and the reflected light thereof is detected by a light detector S1 or the transmitted light thereof is detected by another light detector S2. Vacuum metallizing on the substrate 5 is conducted while monitoring the thickness of the metallized coating. Hereby, when the thickness of the first coating is increased to a predetermined thickness, more formation of coating on the substrate 5 and 16 is prevented by closing a shutter or by other means. Then the holder 8 is rotated by one pitch, and the substrate 16 on the hole 83 is transferred to the hole 15, simultaneously, the evaporation material is changed and the second coating is metallized while being monitored. Similarly, the holder 8 is driven after completion of metallizing of each layer so as to renew the substrate 16, and metallizing is conducted while being monitored.