PURPOSE: To cancel the frequency components of a subject by detecting the changing amounts of the frequency of the subject in a narrow band from two video signals whose focusing states are different.

CONSTITUTION: A photoelectric conversion element 4 converts the optical distribution of the subject into an electric distribution, and A/D converter 5 converts the output signal into a digital signal. Then, a mask shape deciding circuit 6 decides the shape of a mask based on the digital signal, and a mask processing circuit 7 multiples the digital signal by the weight coefficient. Then, a frequency detecting circuit 8 detects the plural frequency components from a mask-processed picture signal. Then, a frequency component rate detecting circuit 9 detects a two frequency component rate by using the pertinent frequency components, and a defocus amount calculating circuit 10 calculates defocus amounts based on the pertinent frequency component rate, each frequency component rate searched from the frequency component/ defocus amount characteristic of an optical system 1, and the table value of a table 11 in which the relation of the defocus amounts is stored. Then, the optical system 1 is driven by a driving circuit 12 based on the pertinent defocus amounts.