Autofocus system and the imaging device

PROBLEM TO BE SOLVED: To accurately obtain a focal position without being influenced by luminance change. SOLUTION: An AF evaluation value calculation circuit 19 comprises: a block division part 30 dividing an imaging signal output from a range-finding area into blocks according to a plurality of areas constituting the range-finding area; first and second frequency component extraction parts 31 and 32 extracting high-order and low-order frequency components from the respective blocks; first and second integration parts 33 and 34 integrating the frequency components extracted by the first and the second frequency component extraction parts 31 and 32 for each block; a maximum value detection part 35 detecting a maximum value from the integrated value for each block obtained by the first integration part 33; an average value calculation part 36 calculating an average value from the integrated value for each block obtained by the second integration part 34; and a difference arithmetic calculation part 37 calculating a difference between the maximum value and the average value. A CPU controls a lens driving part with a difference value calculated by the difference arithmetic calculation part 37 as an AF evaluated value. COPYRIGHT: (C)2008,JPO&INPIT