In the mounting of an electronic component, a holding member is rotated by a predetermined angle prior to actual holding of the electronic parts, thereby to detect a center of the holding member from at least two positions of the rotation angle, and the rotation center of the holding member is found by a calculation based on the detected center of the holding member. The position of the electronic parts against a circuit board then is corrected on the basis of a deviation between the position of the rotation center and the center of the holding member.