to the a d converter 22 in the sequence of a 1 a 2 a n b 1 b 2 b n and supplies a signal ed indicating the end of the storage to the processing circuit 21 the a d converter 22 converts the input analog signal a of the data signals a i and b i to an 8 bit digital information d in synchronism with the conversion signal ad from the drive circuit 23 and supplies the digital information d to the processing circuit 21 the processing circuit 21 sequentially stores the digital data signals a i and b i into the ram and after all of the data signals a i and b i have been stored in the ram determines the defocusing quantity of the imaging lens 1 by a signal proccessing method to be described later and causes the lens driven 25 to focus the imaging lens 1 in accordance with the defocusing quantity when the focusing operation by the device 25 is completed the processing circuit 21 again produces the start signal st to repeat the above operation accordingly while the release button not shown of the camera is held in the first stroke the in focus state discrimination operation and the focusing operation for bringing the imaging lens 1 to the in focus state are repeated the signal processing method of the signal processing circuit 21 in the present embodiment is now explained.