A lens device (3A) is connected to a lens device (3B) to be used in association therewith. The lens device includes a setting unit (25) setting the lens device (3A) as a master, and a control unit (22) driving a control object of the lens device (3A) in response to a control signal input to the lens device (3A) and transmitting the control signal for driving the control object of the lens device (3B) to the lens device (3B) with respect to the control object for which the master has been set by the setting unit. The control unit transmits a mode switching signal which instructs to switch to a slave operating mode that is operated in response to the control signal input from the lens device (3A), to the lens device (3B), with respect to the control object for which the master has been set.