An imaging device, an endoscope apparatus, a method for controlling an imaging device, and the like are disclosed that utilize an imaging optical system designed so that an in-focus object distance is changed along with a change in angle of view, and perform a focus control operation based on phase information from a phase sensor to suppress a situation in which the image acquired during a focus operation flickers, for example. The imaging device includes an imaging optical system that includes a movable lens (240) that simultaneously adjusts the angle of view and the in-focus object distance, an image sensor (260), a plurality of phase sensors, an acquisition section (A/D conversion section (320)) that acquires phase information from the plurality of phase sensors, a lens control section (360) that controls the position of the movable lens (240), and a moving amount calculation section (350) that calculates the moving amount of the movable lens (240) necessary for implementing an in-focus state of an image formed on the image sensor due to light beams that have passed through the imaging optical system, based on a phase difference that is based on the phase information, the lens control section (360) controlling the position of the movable lens (240) based on the moving amount calculated by the moving amount calculation section (350).
