PATTERN DETECTING APPARATUS

An apparatus comprising an image-forming optical system for projecting reflected light from an article to be inspected and travelling on a conveyor onto an imaginary fixed plane to form an image thereon, a similar pattern resembling the pattern of portion of the article to be detected and permitting the passage of reflected light within the same area as the pattern of the portion to be detected, a photoelectric transducer disposed to receive the light passing through the pattern, an arithmetic circuit for calculating the difference between the electrical output level of the photoelectric transducer and an electrical level serving as a reference for judgement, position detecting means for detecting that the article has reached an inspecting position, and a logic circuit for generating an electrical instructing signal in response to a judging output signal from the arithmetic circuit and an article detecting signal from position detecting means.