PURPOSE: To exactly and efficiently detect the mounting position of an object to be detected inclusive of the mounting angle thereof by calculating the mounting position of said object from the various values of the difference in brightness and darkness by the illumination from two light sources.

CONSTITUTION: A monitor camera 5 outputs a video output signal 12 to a pattern detecting circuit 6 when the light of the light source 3 is projected to a chip resistor 2 on a printed circuit board 1. The circuit 6 selects a pattern memory 7, converts the video output signal 12 thereof to a digital value and outputs the same as a detec tion pattern. The detecting circuit 6 selects a pattern memory 8 when the light source 4 is similarly lighted up. The video output signal 12 thereof is then converted to a digital value and is outputted as the detection pattern. The detection patterns stored in the pattern memories 7, 8 are subjected to the determination of the part where the difference in the brightness and darkness is large for each of the picture elements in a comparator circuit 9. The results thereof are stored in a pattern memory 10. Pattern recognition is executed in a pattern recognizing circuit 11. The edges on the side of the light sources 3, 4 are extracted from the hatched part of the compared pattern and the contour of the chip resistance 2 is thereby known. The mounting position is determined by calculating the central point thereof.