PURPOSE: To provide information corresponding to the dimensions characteristic of the type of part by an arrangement wherein one mask member cooperates with one fixed sensor and the mask member masks the fixed sensor in a plurality of combinations.

CONSTITUTION: The recognition apparatus comprises a filter 3 and a detector 4 wherein the filter 3 moves on a machine through a moving unit utilizing a rail and driven by a pneumatic unit. A receiving part 31 projects from the horizontal plane of a table in the machine and abuts against the opposite side of a longitudinal frame member 1. Consequently, the thickness of the longitudinal frame member 1 depends on the distance between a first receiving part 6 and the second movable receiving part 31. The detector 4 is set on a supporting part 41 secured to a mechanical chassis M and a first horizontal shaft 42 transfers at least one mask member 50 secured to the shaft 42. The detector 4 further comprises at least one sensor 60 secured to the securing part of the detector 4.