Even when a bendable section is moved by a large amount to change the field of view observed by an endoscope, an inconvenience such as losing sight of the affected part or feeling a sense of incongruity is reduced. The present invention includes: a switching-instruction step (S6) in which a switching instruction for switching between two different control states of the bendable section provided at a distal end of the insertion section is received； an angle-difference calculation step (S13) in which the angle difference between the current angle (¸ e ) of the bendable section at the time when the switching instruction is received in the switching-instruction step (S6) and the final target angle (¸ g ) of the bendable section in the control state after being switched is calculated； a target calculation step (S4, S15) in which, when the calculated angle difference exceeds a predetermined threshold (¸ th ), a minute angle (”¸), which is smaller than the threshold (¸ th ), is added to the current angle (¸ e ) to calculate the target angle (¸ ref ), and, when the angle difference is less than or equal to the threshold (¸ th ), the angle difference is added to the current angle (¸ e ) to calculate the target angle (¸ ref )； and a driving step (S5) in which the bendable section is driven to the calculated target angle (¸ ref ).
