in calculating circuit 61 difference a1 vi v3 between these focus evaluating values is calculated the difference a1 corresponds to the amount of change of the focus evaluating value generated in 2 fields that is from the second last to the current field focus evaluating values v2 and v4 stored in memories 42 and 44 are applied to fev second change amount calculating circuit 62 and in calculating circuit 62 difference a2 v2 v4 of these focus evaluating values is calculated the difference a2 corresponds to the amount of change of the focus evaluating value generated in 2 fields from three fields before to one field before the current field lens position data l1 and l3 stored in memories 52 and 54 are applied to position change amount calculating circuit 63 and in calculating circuit 63 absolute value b1 l1 l3 of the difference between these data is calculated the value b1 corresponds to the distance of movement of lens 1 during 2 fields that is the second last to the current field lens position data l2 and l4 stored in memories 53 and 55 are applied to second position change amount calculating circuit 64 and in calculating circuit 64 absolute value b2 l2 l4 of the difference between these data is calculated the value b2 corresponds.