An image acquisition apparatus includes a light source configured to emit light, a dividing unit configured to divide the light from the light source into reference light and measurement light, an image forming unit configured to form a tomographic image of a subject based on interfered light in which return light from the subject irradiated with the measurement light and the reference light are interfered, a focus adjusting unit configured to adjust a focus of the measurement light, an optical-path-length adjusting unit configured to adjust an optical path length of the reference light, and a control unit configured to adjust the optical path length of the reference light by controlling the optical-path-length adjusting unit according a change in an optical path length of the measurement light caused by adjustment of the focus using the focus adjusting unit.