To enhance the accuracy of a defocusing amount by obtaining a correction amount at the time of adjustment by using image data where the number of picture elements is larger than at the time of focus detection.

A camera 21 and a chart for adjustment 22 are arranged by leaving the space of a specified distance in between. A lens for adjustment 23 is attached to the camera 21. A device for adjustment 24 is connected to the terminal for adjustment of the camera 21 through a cable. The device 24 fetches picture element data from the image sensor of the focus detector in the camera 21. The device 24 performs specified filtering processing to a pair of image data and calculates a correlation amount for the image data after the filtering processing. The device 24 obtains the deviation by which the correlation amount is minimum and sets it as the correction amount. Thereafter, the device 24 records the obtained correction amount to a correction amount storage part in the camera 21. In such a case, the correction amount is calculated without thinning the picture elements of the image data.