A lens drive unit drives a focus lens. An imaging element obtains an image signal. An evaluation value calculation unit calculates an AF evaluation value from the image signal read out based on an interlace system. A determination unit determines whether the continuous AF evaluation values have a distribution of continuous increases and decreases. If the AF evaluation values are determined to have the distribution of continuous increases and decreases, an in-focus position calculation unit calculates an in-focus position by obtaining an interpolation curve from an intermediate value of the AF evaluation values adjacent to each other, otherwise, calculates the in-focus position by obtaining an interpolation curve of the AF evaluation value. A control unit drives the focus lens to the in-focus position.