1. An imaging apparatus comprising: an output unit including a first output unit being a display unit configured to display images, and a second output unit configured to record or transmit images; a first imaging system including a first lens and a first imaging device configured to generate a first captured image; a second imaging system including a second lens and a second imaging device configured to generate a second captured image; an imaging unit including the first and second imaging systems; an image combining unit configured to combine at least parts from the first and second captured images in order to generate a combined image; a housing including said imaging unit and said display unit; a detecting unit configured to detect whether the housing is set in a horizontal direction or a vertical direction as a state of the imaging apparatus; and a control unit configured to control a size of an output image output by said output unit on the basis of said detected state, wherein the control unit is configured to switch, on the basis of the detected state, a compound-eye imaging operation performed by using the plural imaging devices and a single-eye imaging operation performed by using the first imaging device, and the control unit is configured to determine that, when the single-eye imaging operation is switched to the compound-eye imaging operation, a clock of a predetermined frequency is used for the compound-eye imaging operation and, when the compound-eye imaging operation is switched to the single-eye imaging operation, a clock of a frequency lower than the predetermined frequency is used for the single-eye imaging operation.