A focus detecting device that addresses unstableness in frame rate by performing optimal focus detection depending on a frame rate setting, an AF frame selection setting, and a shooting speed priority/focus priority setting is provided.A focus adjusting device includes means for storing an object signal in an AF sensor; focus detecting means for detecting a defocus amount from the object signal; and focus adjusting means for adjusting the focus of an image taking lens based on the defocus amount. The focus adjusting device also includes a readout time adjusting means for adjusting processing of waiting for a predetermined time since the AF sensor starts storing until the object signal is read out.