An image pickup apparatus that is capable of achieving operating feelings desired by and providing an operability suited to user preference. Pulses are generated by a pulse generating device with rotation of an operating member disposed concentrically with the optical axis of a zoom lens system of a taking lens optical system. A change rate in the operating speed of the operating member is detected. The driving speed of the zoom lens system of the taking lens is determined by referring to an operability parameter table of the relationship between a change rate in the repetition period of output pulses with a change in the rotational speed of the operating member and the driving speed of the zoom lens system of the taking lens.