An imaging device including a camera body and an interchangeable lens unit detachably attached to the camera body, the imaging device comprising: an optical system including a focus lens; an infinite rotation type focus ring; a lens drive part configured to move the focus lens forward and backward in an optical axis direction of the optical system; a setting part allowing a user to set a rotation range of the focus ring; a storage part (106, 109, 120) assigning and storing respective different rotation amounts of the focus ring to multiple positions within a movement stroke of the focus lens in accordance with a rotation range set in the setting part; and a control part driving the lens drive part to move the focus lens depending on a rotation amount of the focus ring to a position corresponding to the rotation amount stored in the storage part (106, 109, 120), characterized in that the imaging device includes a rotation amount storage part storing information of a maximum rotation amount and a minimum rotation amount of the focus ring assignable to multiple positions within the movement stroke, the setting part is configured to enable setting of the rotation range of the focus ring within a range from the maximum rotation amount to the minimum rotation amount stored in the rotation amount storage part when the interchangeable lens unit is attached to the camera body, the imaging device further comprising a display part configured to display multiple rotation amounts within the range from the maximum rotation amount to the minimum rotation amount stored in the rotation amount storage part, wherein the setting part is configured to enable selection of any one of the multiple rotation amounts displayed on the display part as the rotation range of the focus ring. an optical system including a focus lens; an infinite rotation type focus ring; a lens drive part configured to move the focus lens forward and backward in an optical axis direction of the optical system; a setting part allowing a user to set a rotation range of the focus ring; a storage part (106, 109, 120) assigning and storing respective different rotation amounts of the focus ring to multiple positions within a movement stroke of the focus lens in accordance with a rotation range set in the setting part; and a control part driving the lens drive part to move the focus lens depending on a rotation amount of the focus ring to a position corresponding to the rotation amount stored in the storage part (106, 109, 120), characterized in that the imaging device includes a rotation amount storage part storing information of a maximum rotation amount and a minimum rotation amount of the focus ring assignable to multiple positions within the movement stroke, the setting part is configured to enable setting of the rotation range of the focus ring within a range from the maximum rotation amount to the minimum rotation amount stored in the rotation amount storage part when the interchangeable lens unit is attached to the camera body, the imaging device further comprising a display part configured to display multiple rotation amounts within the range from the maximum rotation amount to the minimum rotation amount stored in the rotation amount storage part, wherein the setting part is configured to enable selection of any one of the multiple rotation amounts displayed on the display part as the rotation range of the focus ring.