An image pickup apparatus which is able to obtain an image with high sharpness within a short period of time using a simple structure when operated in a low-temperature environment. A lens unit and a heater are provided in an internal space of a main case, and the internal space is divided into a first closed space and a second closed space via an opening, which is opened and closed by a valve member. A detecting unit detects a temperature in the internal space. An opening and closing unit opens and closes the valve member. A control unit controls opening and closing actions of the valve member.