An objective optical system of an observation unit of the endoscope has a zoom function, and the movable lens for changing a zoom magnification of the objective optical system is controlled to be capable of moving to only a plurality of step positions SP1 to SP4 where specific zoom magnifications are obtained. A control circuit, which controls the movable lens, considers the number N of repetitions and the duration of an on-operation of a zoom switch that instructs the movable lens to move. For example, the movable lens is moved by a step corresponding to the number N of repetitions of the on-operation, and is moved to a step position, which is provided at an end, in a case in which the duration of the on-operation is long.
