To provide a device and method for adjusting focus capable of rapidly bring an object to be focused into focus by suppressing degradation of detection performance of a main object in a low-illuminance condition.

The device for adjusting focus includes a focus lens, a photoelectric conversion means, an extraction means, and a control means. The photoelectric conversion means converts an object image imaged by the focus lens to an electric signal. The extraction means extracts a signal component of a specific frequency band from an output signal of the photoelectric conversion means. The control means executes a first operation for identifying an object region to be focused by executing an AF scan operation before imaging preparation, and executes a second operation different from the first operation by executing the AF scan operation to execute a focusing operation in the imaging preparation. When the brightness of the object is smaller than a first threshold value before the imaging preparation, a third operation different from the first operation is executed.

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