PURPOSE: To measure the thickness of the non-magnetic film without contact continuously by providing a throttle in a respective air path wherein air which is pressurized into a contant positive pressure is flowed and dually constituting bridge type air micrometers in the downstream.

CONSTITUTION: A metal plate 22 which is not painted is placed on a specified position. The position of a base 16 is adjusted by a micrometer 3 so that the indication of a film thickness measuring gage 23 becomes zero. The air is sent to the bridge type air micrometers. Then the positions of a probe 20 and a measuring nozzle 10c are adjusted so that the measuring gage 23 indicates the scale of 100μ through the micrometer 3 and an adjusting screw 8. Thereafter the painted metal plate 22 is placed on the specified position. Then back pressure p1 rises, bellow 7b rise, a back pressure p3 of a nozzle 10b is lowered, back pressure p2 of a nozzle 10a rises, and a rotary arm 14 is rotated clockwise. As a result, a block 19 is moved, and a gap g3 is expanded up to 100μ and balanced. The value which is the sum of 100μ and the thickness of non-magnetic film 21 is indicated. Thus the film thickness (d) is measured without contact.